Low-noise optical probes for reducing ambient noise

ABSTRACT

An optical probe, which is particularly suited to reduce noise in measurements taken on an easily compressible material, such as a finger, a toe, a forehead, an earlobe, or a lip, measures characteristics of the material. A neonatal and adult disposable embodiment of the probe include adhesive coated surfaces to securely affix the probe onto the patient. In addition, the surface of the probe is specially constructed to reduce the effect of ambient noise.

REFERENCE TO RELATED APPLICATIONS

The present application claims priority benefit under 35 U.S.C. §120 to,and is a continuation U.S. patent application Ser. No. 10/957,843, filedOct. 4, 2004 entitled “Low-Noise Optical Probes for Reducing AmbientNoise,” now U.S. Pat. No. 7,483,730, which is a continuation of U.S.patent application Ser. No. 10/260,049, filed Sep. 27, 2002 entitled“Low-Noise Optical Probes for Reducing Ambient Noise,” now U.S. Pat. No.6,813,511, which is a continuation of U.S. patent application Ser. No.09/898,990, filed Jul. 3, 2001 entitled “Low-Noise Optical Probes forReducing Light Piping,” now U.S. Pat. No. 6,792,300, which is acontinuation of U.S. patent application Ser. No. 09/094,202, filed Jun.9, 1998 entitled “Low-Noise Optical Probes,” now U.S. Pat. No.6,256,523, which is a continuation of U.S. patent application Ser. No.08/543,789, filed Oct. 16, 1995 entitled “Low Noise Optical Probes,” nowU.S. Pat. No. 5,782,757. The present application incorporates theforegoing disclosures herein by reference.

FIELD OF THE INVENTION

The present invention relates to low-noise, disposable and reusableoptical probes which may be used to sense optical energy passed througha medium to determine the characteristics of the medium.

BACKGROUND OF THE INVENTION

Energy is often transmitted through or reflected from a medium todetermine characteristics of the medium. For example, in the medicalfield, instead of extracting material from a patient's body for testing,light or sound energy may be caused to be incident on the patient's bodyand transmitted (or reflected) energy may be measured to determineinformation about the material through which the energy has passed. Thistype of non-invasive measurement is more comfortable for the patient andcan be performed more quickly.

Non-invasive physiological monitoring of bodily function is oftenrequired. For example, during surgery, blood pressure and the body'savailable supply of oxygen, or the blood oxygen saturation, are oftenmonitored. Measurements such as these are often performed withnon-invasive techniques where assessments are made by measuring theratio of incident to transmitted (or reflected) light through a portionof the body, for example a digit such as a finger, or an earlobe, or aforehead.

Transmission of optical energy as it passes through the body is stronglydependent on the thickness of the material through which the lightpasses, or the optical path length. Many portions of a patient's bodyare typically soft and compressible. For example, a finger comprisesskin, muscle, tissue, bone, blood, etc. Although the bone is relativelyincompressible, the tissue, muscle, etc. are easily compressible withpressure applied to the finger, as often occurs when the finger moves.Thus, if optical energy is made incident on a finger and the patientmoves in a manner which distorts or compresses the finger, the opticalpath length changes. Since a patient generally moves in an erraticfashion, the compression of the finger is erratic. This causes thechange in optical path length to be erratic, making the absorptionerratic, resulting in a difficult to interpret measured signal.

Many types of non-invasive monitoring devices have been developed to tryto produce a clear and discernable signal as energy is transmittedthrough a medium, such as a finger or other part of the body. In typicaloptical probes a light emitting diode (LED) is placed on one side of themedium while a photodetector is placed on an opposite side of themedium. Many prior art optical probes are designed for use only when apatient is relatively motionless since, as discussed above, motioninduced noise can grossly corrupt the measured signal. Typically, probesare designed to maximize contact between the LED and the medium and thephotodetector and the medium to promote strong optical coupling betweenthe LED, the medium, and the photodetector, thereby generating a strongoutput signal intensity. In this way, a strong, clear signal can betransmitted through the medium when the patient is generally motionless.

For example, U.S. Pat. No. 4,880,304 to Jaeb, et al. discloses anoptical probe for a pulse oximeter, or blood oxygen saturation monitor,comprising a housing with a flat lower face containing a centralprotrusion in which a plurality of light emitting diodes (LEDs) and anoptical detector are mounted. When the probe is placed on the patient'stissue, the protrusion causes the LEDs and the detector to press againstthe tissue to provide improved optical coupling of the sensor to theskin. In another embodiment (FIGS. 4 a and 4 b in the Jaeb patent), theLEDs and the detector are arranged within a central chamber, generallyhorizontal with respect to the tissue on which the probe is placed. Aset of mirrors or prisms causes light to be directed from the LEDs ontothe tissue through a polymer sealant within the chamber, the sealantproviding a contact with the tissue for good optical coupling with thetissue.

U.S. Pat. No. 4,825,879 to Tan, et al. discloses an optical probewherein a T-shaped wrap, having a vertical stem and a horizontal crossbar, is utilized to secure a light source and an optical sensor inoptical contact with a finger. The light source is located in a windowon one side of the vertical stem while the sensor is located in a windowon the other side of the vertical stem. The finger is aligned with thestem and the stem is bent such that the light source and the sensor lieon opposite sides of the finger. Then, the cross bar is wrapped aroundthe finger to secure the wrap, thereby ensuring that the light sourceand the sensor remain in contact with the finger to produce good opticalcoupling.

U.S. Pat. No. 4,380,240 to Jobsis, et al. discloses an optical probewherein a light source and a light detector are incorporated intochannels within a slightly deformable mounting structure which isadhered to a strap. Annular adhesive tapes are placed over the sourceand the detector. The light source and detector are firmly engaged witha bodily surface by the adhesive tapes and pressure induced by closingthe strap around a portion of the body. An alternative embodimentprovides a pressurized seal and a pumping mechanism to cause the body tobe sucked into contact with the light source and detector.

U.S. Pat. No. 4,865,038 to Rich, et al. discloses an optical probehaving an extremely thin cross section such that it is flexible. A dieLED and a die photodetector are located on a flexible printed circuitboard and encapsulated by an epoxy bead. A spacer, having circularapertures positioned in alignment with the LED and photodetector, isplaced over the exposed circuit board. A transparent top cover is placedover the spacer and is sealed with a bottom cover placed under thecircuit board, thereby sealing the probe from contaminants. A spine maybe added to strengthen the device. The flexibility of the device allowsit to be pinched onto the body causing the epoxy beads over the LED andthe photodetector to protrude through the apertures in the spacer andpress against the top cover such that good optical contact is made withthe body.

U.S. Pat. No. 4,907,594 to Muz discloses an optical probe wherein a dualwall rubberized sheath is fit over a finger. A pump is located at thetip of the finger such that a pressurized chamber may be formed betweenthe two walls, thereby causing an LED and a photodetector located in theinner wall to be in contact with the finger.

Each of the above described optical probes is designed to cause a strongmeasured signal at the photodetector by optimizing contact between theLED, the patient, and the probe. However, this optimization forcescompressible portions of the patient's body to be in contact withsurfaces which compress these portions of the patient's body when thepatient moves. This can cause extreme changes in the thickness ofmaterial through which optical energy passes, i.e., changes in theoptical path length and changes due to scattering as a result of venousblood movement during motion. Changes in the optical path length canproduce enough distortion in the measured signal to make it difficult orimpossible to determine desired information.

Furthermore, demand has increased for disposable and reusable opticalprobes which are suitably constructed to provide low-noise signals to beoutput to a signal processor in order to determine the characteristicsof the medium. Many difficulties relating to motion-induced noise havebeen encountered in providing such an optical probe inexpensively.Furthermore, such probes tend to be difficult to use in certainapplications, such as, applications where a patient's finger may move orshift during measurement, or, in a more extreme case, when the opticalprobe is employed on small children who typically do not sit stillduring the measurement process.

Thus, a need exists for a low-cost, low-noise optical probe which iseasy to use under adverse conditions, and for a method of manufacturingsuch a probe. More specifically, a need exists for a probe which reducesmotion induced noise, or motion artifacts, during measurement of asignal while still generating a transmitted or reflected signal ofsufficient intensity to be measured by a detector.

SUMMARY OF THE INVENTION

The present invention involves a probe for use in non-invasive energyabsorption (or reflection) measurements. One aspect of the presentembodiment involves an optical probe for non-invasive measurement ofcharacteristics of a medium, wherein the prove has an emitter whichtransmits optical radiation and a detector configured to detect theoptical radiation transmitted by the emitter. The probe also has aflexible circuit assembly having circuit paths for connection with theemitter and the detector. A substrate forms a surface of the flexcircuit assembly between the detector and the emitter. The substrate isconstructed to minimize light piping from the emitter to the detector.

In one embodiment, the probe further has a flexible backing supportingthe flex circuit, the flexible backing being configured to attach theoptical probe to the medium. Advantageously, a an optical cavity isprovided for the detector.

In one advantageous embodiment, the flexible circuit assembly issufficiently flexible to provide spring action to minimize opticaldecoupling between the emitter and the detector due to perturbations ofthe medium. Advantageously, a flexible backing supporting the flexcircuit is configured to affix the optical probe to the medium. Also, inone preferred embodiment, the flex circuit has an optical obstructionbetween the emitter and the detector.

In one preferred embodiment, the optical obstruction comprising anaperture through the flex circuit configured to receive a fingertip whenthe optical probe is affixed to a finger. The aperture stabilizes thefinger within the probe so as to reduce optical decoupling between theemitter and the detector.

Preferably, the probe has an optical cavity containing the detector. Inone advantageous embodiment, the optical cavity containing the detectoris coated with a material which absorbs ambient light or the cavity ismade from an ambient light absorptive material.

A further aspect of the present invention involves an probe for thenon-invasive measurement of characteristics of a medium. According tothis aspect, the optical probe has an emitter which transmits opticalradiation and a detector configured to detect the optical radiationafter attenuation through the medium. Again, a flexible circuit assemblyextending between the emitter and the detector has electrical circuitpaths for the detector and the emitter. A cushion positioned between thedetector and the emitter along the flexible circuit is also provided.The cushion is preferably formed in the flexible circuit between theemitter and the detector so that the cushion abuts a patient's fingertipwhen the optical probe is attached to the fingertip.

Another aspect of the present invention involves an optical probe forthe non-invasive measurement of characteristics of a medium, wherein theprobe has a substrate which forms a surface for the probe such that thesubstrate is constructed to have a V-configuration with the emitter anddetector positioned on opposite branches of the V-configuration. Thisconfiguration is advantageous for use with a newborn baby.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic medium comprising N differentconstituents.

FIG. 2 a illustrates an ideal plethysmographic signal that would bemeasured by the optical probe of the present invention when utilized forpulse oximetry.

FIG. 2 b illustrates a realistic signal measured by the optical probe ofthe present invention when utilized for pulse oximetry.

FIG. 3 is a perspective view of a probe of the present invention havinga single segment chamber.

FIG. 4 is a cross-sectional view of an optical probe of the presentinvention illustrating a single segment chamber having a detector withinit.

FIG. 5 is a cross-sectional view of a probe of the present inventionhaving a detector resting on a shell of base material.

FIG. 6 is a cross-sectional view of a probe of the present inventionincorporating a light collecting lens.

FIG. 7 is a cross-sectional view of a probe of the present inventionillustrating a single segment chamber having an LED within it.

FIG. 8 is a cross-sectional view of a probe of the present inventionincorporating a collimating lens assembly.

FIG. 9 is a cross-section view of a probe of the present inventionwherein the LED and the detector are not aligned along the central axisof the chamber.

FIG. 10 is a perspective view of another embodiment of a probe of thepresent invention having a two segment chamber.

FIG. 11 is a cross-sectional view of another embodiment of the probe ofFIG. 10 incorporating a two segment chamber having a detector within it.

FIG. 12 is a cross-sectional view of another embodiment of the probe ofFIG. 10 incorporating a light collecting lens in a two segment chamber.

FIG. 13 is a perspective view of a probe of the present invention havinga three segment chamber.

FIG. 14 is a cross-sectional view of the probe of FIG. 13 incorporatinga three segment chamber having a detector within it.

FIG. 15 is a cross-sectional view of another embodiment of the probe ofFIG. 13 incorporating a light collimating lens.

FIG. 16 is a perspective view of a probe of the present inventionspecifically designed to be used with a digit.

FIG. 17 illustrates a schematic finger comprising fingernail, skin,bone, tissue, muscle, blood, etc.

FIG. 18 is a cross-section view of the probe of FIG. 16.

FIG. 19 is a longitudinal cross-sectional view of the probe of FIG. 16.

FIG. 20 is a cross-sectional view of another embodiment of the probe ofFIG. 16 incorporating a light collecting lens.

FIG. 21 is a cross-sectional view of a probe of the present inventiondesigned to be utilized for reflectance measurements.

FIG. 22 is a cross-sectional view of a probe which is advantageouslyused for non-invasive measurements when a material is compressible onmore than one side. The probe has two bases, each with a chamber tohouse a detector or an energy source and thereby reduce motionartifacts.

FIG. 23 is a cross-sectional view of a probe having a generallycone-shaped chamber with a reflective surface which advantageouslycauses energy to be concentrated, or “funneled,” onto the surface of adetector within the chamber, improving the measured signal.

FIG. 24 is a schematic of one system which may advantageously employ aprobe of the present invention.

FIG. 25 is a cross-sectional view of a probe wherein the aperture isfilled with a compressible scattering medium.

FIG. 26 is a cross-sectional view of a probe wherein the LED is spacedfrom the material to be measured by a transmission assembly having ascattering medium interposed between the LED and the material.

FIG. 27 is a cross-sectional view of a probe wherein a scattering mediumis interposed between the LED and the material as well as between thematerial and the photodetector.

FIG. 28 is a cross-sectional view of a preferred embodiment of a probein accordance with the present invention having an immersion lens forthe photodetector and for the LED and having scattering mediuminterposed between the LED and the test material as well as between thetest material and the photodetector.

FIGS. 29A-29B are perspective views illustrating the use of oneembodiment of the disposable optical probe of the present invention tomeasure the characteristics of a human fingertip.

FIG. 30 is a flow chart which details a method of manufacturing thelow-noise optical probe shown in FIGS. 29A-29B.

FIG. 31 depicts a first step of the manufacturing process, whereinmultiple rows of flex circuit panels are etched onto a flex circuitpanel comprising, for example, copper/MYLAR™, copper/CAPTON™, orconductive ink/MYLAR™.

FIG. 31A depicts the placement of detector shields on pressure sensitiveadhesive at detector end of the flex circuit.

FIG. 31B illustrates a second step in the manufacturing process, whereincomponents are placed and soldered onto the flex circuits of FIG. 31.

FIGS. 32A and 32B illustrate a third step in the manufacturing process,wherein the flex circuits are placed onto a strip of flex circuit shieldmaterial.

FIGS. 33A and 33B depict a fourth step of the manufacturing process,wherein the flex circuit assemblies are die cut and the shields arefolded over the flex circuits to provide the completed flex circuitassemblies.

FIG. 34 illustrates a fifth step of the manufacturing process, wherein aconnector tab and a detector cavity are placed onto a sheet of basematerial.

FIG. 35 depicts a sixth stage of the manufacturing process, wherein theflex circuit assembly is positioned on the base material.

FIG. 36 illustrates a seventh step in the manufacturing process, whereina cover is placed over the detector cavity.

FIG. 37 illustrates an eighth step of the manufacturing process, whereinface stock is placed over the flex circuit assembly on the basematerial.

FIG. 38 illustrates a ninth step of the manufacturing process, whereinthe optical probe is die cut to the final shape shown in FIG. 29 a.

FIGS. 39A-39C illustrate an optical cavity in detail.

FIGS. 40A and 40B illustrate the application of the a neonatal probemade in accordance with the present invention.

FIG. 41 is a flow chart which details the general method used formanufacturing a neonatal disposable optical probe in accordance with asecond embodiment of the present invention.

FIG. 42 illustrates a first step of the manufacturing process for aneonatal embodiment of the low-noise optical probe, wherein a firstlayer of tape is laid out.

FIG. 43 illustrates a second step in the manufacturing process for theneonatal probe, wherein a second elongated layer of tape is laid outover the first layer of FIG. 41.

FIGS. 44A-44C illustrate an optical cavity in detail.

FIGS. 45A-45C illustrate the manufacture of the neonate flex circuitassembly.

FIG. 46 illustrates a third step in the manufacturing process for theneonatal probe, wherein the flex circuit is laid out with a connector aswell as an optical probe onto the second layer of tape.

FIG. 47 illustrates a fourth step in the manufacturing process of theneonatal probe, wherein the third and fourth layers of tape are laidover the flex circuit.

FIG. 48 illustrates a fifth step in the manufacturing process whereinthe neonatal probe is die-cut to the final shape.

FIGS. 49 and 50 depict an alternative embodiment of the neonatal probewherein a soft, hospital wrap is used to affix the probe to a newborn'sfoot.

FIGS. 51-54 illustrate an alternative method of manufacturing theneonate probe.

FIGS. 55A-55C depict a cover which is affixed over the optical cavity.

FIG. 56 depicts a clip-on version of the optical probe.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Examination of a material is often advantageous, especially when it isdifficult or expensive to procure and test a sample of the material. Forexample, in physiological measurements, it is often desirable to monitora patient without drawing of blood or tissue from the patient. The knownproperties of energy absorption as energy propagates through a materialmay be used to determine information about the material through whichthe energy has passed. Energy is made incident on a material, and ameasurement is made of energy either transmitted by or reflected fromthe material.

The amplitude of the measured signal is highly dependent on thethickness of the material through which the energy passes, or theoptical path length, as well as other properties such as the erraticmovement of venous blood during motion. A schematic medium 20 comprisingN different constituents A₁ through A_(N) is shown in FIG. 1. Energytransmitted through the medium 20 is approximately attenuated accordingto the equation:

$\begin{matrix}{I \approx {I_{0}{\mathbb{e}}^{- {\sum\limits_{i = 1}^{N}{ɛ_{i}c_{i}x_{i}}}}}} & (1)\end{matrix}$

where ε₁ is the absorption coefficient of the i^(th) constituent; x_(i)is the thickness of the i^(th) constituent through which light energypasses, or the optical path length of the i^(th); and c_(i) is theconcentration of the i^(th) constituent in thickness x_(i).

Since energy absorption is strongly dependent on the thicknesses of theconstituents A₁ through A_(N) which make up the medium 20 through whichthe energy passes, when the thickness of the medium 20 changes, due tomotion for example, the thicknesses of the individual constituents A₁through A_(N) change. This causes the absorption characteristics of themedium 20 to change.

Often a medium 20 is under random or erratic motion. For example, if themedium 20 is an easily compressible portion of a patient's body, such asa digit, and the patient moves, the medium 20 compresses erraticallycausing the individual thicknesses X₁ through X_(N) of the constituentsA₁ through A_(N) to vary erratically. This erratic variation may causelarge excursions in the measured signal and can make it extremelydifficult to discern a desired signal, as would be present withoutmotion induced noise, or motion artifacts.

For example, FIG. 2 a illustrates an ideal desired signal waveform,labeled Y, measured in one application of the present invention, namelypulse oximetry. FIG. 2 b illustrates a more realistic measured waveformS, also measured in a pulse oximetry application, comprising the idealdesired signal waveform Y plus motion induced noise, n, i.e. S=Y+n. Itis easily seen how motion artifacts obscure the desired signal portionY.

FIG. 3 is a perspective view of one embodiment of an optical probe 100of the present invention which greatly diminishes the effects of motionartifacts on the measured signal. FIG. 4 shows a cross-sectional view ofthe optical probe 100 of the present invention taken along line 4-4 inFIG. 3. For clarity in the perspective view of FIG. 3, a material 128 onwhich measurements are to be taken is not shown placed adjacent theprobe 100. However, the material 128 on which measurements are to bemade is shown in FIG. 4. As illustrated in FIGS. 3 and 4, a base 110,having a top 112, a bottom 114, a forward end 116, and a rear end 118,is made of a material which is preferably rigid and opaque. It will beunderstood, however, that the probe 100 may be made of materials whichmay be rigid, resilient, opaque, or transparent, for example.

An aperture 120 is formed in the top 112 of the base 110. Typically, theaperture 120 is located at a point between one-quarter and one-half ofthe length of the base 100. The aperture 120 may be of any shape,including but not limited to circular, square, or triangular. Theaperture 120 forms the opening to a chamber 122 which may also be of anyshape. In one embodiment, a lateral cross-section (not shown) of thechamber 122 is the same shape as the aperture. A central axis 124 of thechamber 122 is defined by a line aligned perpendicular to the aperture120 and extending generally through a central portion of the aperture120.

In the embodiment of FIG. 4, a light source 130, typically a lightemitting diode (LED), is affixed adjacent the material 128, alignedalong the central axis 124 of the chamber 122 opposite the chamber 122.Typically, an adhesive such as medical tape is used to affix the LED 130to the material 128. A detector 126, such as a photodetector, is placedwithin the chamber 122. A central portion of the photodetector 126 isgenerally aligned with the central axis 124 of the chamber 122,typically at the bottom 114 of the chamber 122. The photodetector 126may be fixed within the chamber 122 according to a number of differentmethods, including but not limited to adhesive, a press fit, or clearepoxy resin which transmits light over a range of wavelengths ofinterest. Typically, no matter how the photodetector 126 is held withinthe chamber 122, the bottom surface 114 of the chamber 122 is madeopaque either via the press fit or via paint or tape, for example.

It is often the case that materials 128 on which absorption measurementsare performed are, at least in part, easily compressible. Easilycompressible portions of the material 128 are placed directly adjacent(i.e., above) the chamber 122. The area surrounding the aperture 120supports the material covering the chamber 122. The chamber 122 is wideenough that any compressible portion of the material 128 located abovethe aperture 120 may intrude into the chamber 122. Thus, the material122 may rest above or penetrate slightly into the chamber 122 and isthereby shielded from perturbations which compress the material 128,such as pressure caused when the material 128 is touched.

In the present embodiment, the depth of the chamber 122 may range from0.5 mm to 10 mm in depth, with 2-4 mm preferred, and 3-4 mm morepreferred. Similarly, the diameter of the aperture 120 may, in thepresent embodiment, range from 3 mm to 20 mm, as required by thespecific application. For instance, the aperture would be smaller forneonates than for adults. These sizes have been found to be effective inreducing perturbations and compression of the material 128, when thematerial is human skin.

The chamber 122 is deep enough that the photodetector 126 and the bottom114 of the chamber 122 do not come into contact with the easilycompressible portion of the material 128, even when the material 128 iscaused to move. Thus, along the central axis 124 of the chamber 122nothing comes into physical contact with the easily compressible portionof the material 128 and causes it to compress. With little or nocompression of the material 128 in this region, the thickness of thematerial 128, or the optical path length of light energy propagatingthrough the material 128, is substantially stabilized in the field ofview of the photodetector. The movement of venous blood due tocompression is also minimized in the field of view of the photodetector.

The LED 130 emits light at a known wavelength. The light propagatesthrough the material 128 and an attenuated signal is transmitted intothe chamber 122 to be received by the photodetector 126. As light fromthe LED 130 propagates through the material 128, it is scattered by thematerial 128 and is thus transmitted into the chamber 122 over a broadrange of angles in a very complex manner. Thus, some of the light iscaused to be incident on the opaque walls 123 of the chamber 122 and isabsorbed. Although the signal travels through a greater optical distanceto reach the photodetector 126 at the bottom 114 of the chamber 122 thanif the photodetector 126 were immediately adjacent the material 128,thus eliminating direct coupling between the photodetector 126 and thematerial 128, the resulting degradation to signal intensity iscompensated for by the stabilization of the optical path length and theresultant reduction of noise in the measured signal. The photodetector126 produces an electrical signal indicative of the intensity of lightenergy incident on the photodetector 126. The electrical signal is inputto a processor which analyzes the signal to determine characteristics ofthe media 128 through which the light energy has passed.

The opaque quality of the base 110 absorbs ambient light which caninterfere with the signal measured at the photodetector 126. Thisfurther improves signal quality. Further, the opaque bottom 114 of thechamber 122 protects the photodetector 126 from ambient light which canobscure the desired signal measured at the photodetector 126. Thus, anaccurate measurement of the intensity of the attenuated signal may bemade at the photodetector 126.

An alternative embodiment of the chamber 122 is shown in frontalcross-section in FIG. 5. A shell 131 of base 110 material covers thebottom 114 of the chamber 122. The photodetector 126 is mounted on theshell 131, within the chamber 122, generally aligned with the LED 130.The photodetector 126 is electrically connected to a processor through asmall hole (not shown) in the shell 131. The shell 131 shields thephotodetector 126 from ambient light which can seriously degrade thesignal-to-noise ratio of the signal measured at the photodetector 126.It will be understood that the bottom 114 of the chamber 122 may beformed with or without the shell in any embodiment of the probe of thepresent invention.

FIG. 6 shows a frontal cross sectional view of another embodiment of theprobe 100 of the present invention wherein a light collecting lens 132is placed within the chamber 122, between the material 128 which restsabove or enters into the chamber 122 and the photodetector 126. The lens132 has one generally planar surface 132 a aligned parallel to theaperture 120 in the top 112 of the base 110, located deep enough withinthe chamber 122 that any material 128 which intrudes into the chamber122 does not contact the planar surface 132 a of the lens 132. Anothersurface 132 b of the lens 132 is generally convex having its apexdirected toward the photodetector 126 in the bottom 114 of the chamber122. The lens 132 may be held in the chamber 122 by a number of means,including but not limited to optical adhesive, a lens retaining ring, ora press fit. The chamber 122 functions in the same manner as describedabove to stabilize the optical path length and reduce motion artifacts.The light collecting lens 132 gathers much of the light which wasscattered as it was transmitted through the material 128 and causes itto be incident on the photodetector 126. This produces a strongermeasured signal.

FIG. 7 shows another embodiment of the probe 100 of the presentinvention wherein the positions of the photodetector 126 and the LED 130are interchanged. The LED 130 is placed within the chamber 122,typically at the bottom 114 of the chamber 122, generally aligned withthe central axis 124 of the chamber 122. The LED 130 may be fixed withinthe chamber 122 according to a number of different methods, includingbut not limited to a press fit, adhesive, or clear epoxy resin whichtransmits light over a range of wavelengths of interest, such as aroundthe wavelength which the LED emits. Again, a material 128 is placed onthe base 110 having a compressible portion of the material 128 locateddirectly above the chamber 122. The photodetector 126 is attached to thematerial 128, opposite the LED 130, such that the LED 130, thephotodetector 126, and the chamber 122 are aligned along the centralaxis 124 of the chamber 122. The photodetector 126 is typically attachedby an opaque material. For example, the photodetector 126 may beattached to the material 128 with opaque tape, thereby limiting signaldegradation caused by ambient light. The photodetector 126 is, again,electrically connected to a processor.

The probe 100 of this embodiment functions substantially identically tothe embodiment of the probe 100 having the photodetector 126 housed inthe chamber 122. The chamber 122 stabilizes the optical path length byallowing easily compressible portions of the material 128 to rest aboveor intrude into the chamber 122, thereby stabilizing the optical pathlength and substantially reducing motion artifacts. This is trueregardless of whether the photodetector 126 or the LED 130 is housedwithin the chamber 122.

FIG. 8 shows a cross-sectional view of another embodiment of the probe100 of the present invention wherein the LED 130 is located within thechamber 122. A collimating lens assembly 140 is placed within thechamber 122, between the material 128 which rests above or enters intothe chamber 122 and the LED 130. Collimating lens assemblies 140 arewell known in the art and, thus, the lens assembly 140 is representedschematically in the FIG. 8. The collimating lens assembly 140 islocated deep enough within the chamber 122 that any material 128 whichintrudes into the chamber 122 does not contact the lens assembly 140.The lens assembly 140 may be held in the chamber 122 by a number ofmeans, including but not limited to optical adhesive, a lens retainingring, or a press fit. The chamber 122 functions in the same manner asdescribed above to stabilize the optical path length and reduce motionartifacts. The collimating lens assembly 140 causes light from the LED130 to be focused on the material 128 above the chamber 122, thusproviding a less scattered signal transmitted onto the photodetector 126surface, thereby utilizing the photodetector 126 more effectively.

FIG. 9 shows another embodiment of the probe 100 of the presentinvention wherein the LED 130 and the photodetector 126 are not alignedalong the central axis 124 of the chamber 122. Light is scattered withinthe material 128, causing at least a portion of the light emitted by theLED 130 to reach the photodetector 126 for measurement. As long as lightemitted by the LED 130 and scattered by the material 128 reaches thephotodetector 126 with great enough intensity to be measured, the LED130 and the photodetector 126 need not be aligned. While alignment ofthe LED 130 and the photodetector 126 along the same axis causes thelight emitted by the LED 130 to reach the photodetector 126 moredirectly, it is not necessary for operation of the probe of the presentinvention. In some applications, misalignment may even be advantageous.It will be understood that this is true for any embodiment of the probeof the present invention. Additionally, it will be understood that aphotodetector 126 which fills the width of the chamber 122 isadvantageous in that more of the light directed into the chamber 122will be incident on the surface of the photodetector 126, resulting in astronger measured signal. However, any size photodetector 126 whichacquires enough energy to produce an adequately strong measured signalis acceptable. It will be understood that this is true for anyembodiment of the probe of the present invention.

A perspective view of another embodiment of a probe 200 of the presentinvention comprising a multi-segment chamber 222 is shown is FIG. 10.FIG. 11 shows a cross-sectional view of the probe 200 of the presentinvention taken along line 11-11 in FIG. 10. For clarity in theperspective view of FIG. 10, a material 228 on which measurements are tobe taken is not shown placed adjacent the probe 200. However, thematerial 228 is shown adjacent the probe 200 in FIG. 11.

As illustrated in FIGS. 10 and 11, a base 210, having a top 212, abottom 214, a forward end 216, and a rear end 218, is made of a materialwhich is preferably rigid and opaque. It will be understood, however,that the probe 200 may be made of materials which may be rigid,resilient, opaque, or transparent, for example. An aperture 220 of anyshape is formed in the base 210, similar to the aperture 120 describedabove in conjunction with the probe 100 of FIGS. 3 through 9. Theaperture 220 forms the opening to a stabilizing segment 222 a of themultiple segment chamber 222. A lateral cross-section (not shown) of thestabilizing segment 222 a of the chamber 222 is typically the same shapeas the aperture 220. Walls 223 a of the stabilizing segment 222 a aregenerally perpendicular to the aperture 220. A central axis 224 of thechamber 222 is defined by a line aligned generally perpendicular to theaperture 220 and extending generally through a central portion of theaperture 220 and the chamber 222.

A mounting segment 222 b is located directly adjacent and below thestabilizing segment 222 b, connected to the stabilizing segment 222 b bya border 225. The mounting segment 222 b shares the central axis 224 ofthe stabilizing segment 222 a and is typically of smaller width. Walls223 b of the mounting segment 222 b are generally parallel to thecentral axis 224. The mounting segment 222 b may extend through thebottom 214 of the base 210, as shown in FIG. 11, or the mounting segment222 b may extend to just above the bottom 214 of the base 210, leaving ashell (not shown) of base 210 material at the bottom 214 of the chamber222.

A photodetector 226 is placed in the mounting segment 222 b of thechamber 222, typically at the bottom 214 of the mounting segment 222 b,having a central portion of the photodetector 226 generally aligned withthe central axis 224 of the chamber 222. The mounting segment 222 b ofthe chamber 222 is deep enough that the photodetector 226 does notpenetrate into the stabilizing segment 222 of the chamber 222. Thephotodetector 226 may be fixed within the chamber 222 according to anumber of different methods, including but not limited to adhesive, apress fit, or a clear epoxy resin which transmits light over a range ofwavelengths of interest. In this embodiment, the bottom 214 of thechamber 222 is made opaque via paint or tape, for example, or by leavinga shell (not shown) of base 210 material at the bottom 214 of thechamber 222 when the chamber 222 is formed. The photodetector 226 iselectrically connected to a processor, similarly to the photodetector126 in the previous embodiment of the probe 100 of the presentinvention.

An energy absorbing material 228 (the material under test) is placedover the base 210 as shown in the cross section of FIG. 11. A portion ofthe material 228 may rest above the chamber 222. Additionally, thestabilizing segment 222 a of the chamber 222 is wide enough that anyeasily compressible portion of the material 228 may intrude into thestabilizing segment 222 a of the chamber 222. The stabilizing segment222 a of the chamber 222 is deep enough that the portion of the material228 which enters into the stabilizing segment 222 a does not contactmatter within the stabilizing segment 222 a which might causecompression, even when the material 228 is caused to move.

A light emitting diode (LED) 230 is affixed adjacent to the material228, opposite the aperture 220. The LED 230 is advantageously alignedalong the central axis 224 to optimize the amount of light incidentdirectly through the material 228 onto the photodetector 226. However,it will be understood that the positions of the photodetector 226 andthe LED 230 could be interchanged as discussed in conjunction with FIG.7. Additionally, a collimating lens assembly (not shown) could be addedto the chamber 222 as discussed in conjunction with FIG. 8. Thecollimating lens assembly may be held in the chamber 222 similarly to alight collecting lens 232 discussed below. Further, it will beunderstood that the LED 230 and the photodetector 226 could beunaligned, as discussed in conjunction with FIG. 9.

As light from the LED 230 propagates through the material 228, it isscattered by the material 228 and is thus transmitted into the chamber222 over a broad range of angles. Thus, some of the light is caused tobe incident on the opaque walls 223 a and 223 b of the chamber 222 andis absorbed. However, the advantageous alignment of the photodetector226 and the LED 230 along the central axis 224 causes a large percentageof the light to be incident on the surface of the photodetector 226.Since the material 228 remains substantially uncompressed above andwithin the stabilizing segment 222 a, the thickness through which thelight travels, or the optical path length, is substantially stabilized.Thus, the signal-to-noise ratio of the measured signal is improved bythe suppression of motion artifacts due to the chamber 222.

In another embodiment of the probe 200, a light collecting lens 232 isinserted within the chamber 222, as shown in cross-section in FIG. 12.The lens 232 is advantageously supported at the border 225 between thestabilizing segment 222 a and the mounting segment 222 b. The lens maybe held in place by a number of means, including but not limited to anoptical adhesive, a lens retaining ring, or a press fit. The lens 232has a generally planar surface 232 a aligned with the border 225 betweenthe stabilizing segment 222 a and the mounting segment 222 b and agenerally convex surface 223 b extending into the mounting segment 222 bof the chamber 222. The stabilizing segment 222 a of the chamber 222 isdeep enough that the lens 232 does not contact any of the compressiblematerial 228 which may have intruded into the chamber 222.

The lens 232 collects light which is incident on the planar surface 232a. Much of the light which is incident on this surface 232 a at angleswhich would be absorbed by the walls 223 a and 223 b of the chamber 222if the lens were not present is now directed toward the photodetector226. Thus, a greater percentage of the light transmitted through thematerial 228 is caused to be incident on the photodetector 226,resulting in a stronger measured signal.

A perspective view of another embodiment of the probe 300 of the presentinvention which incorporates a chamber 322 having three segments 322 a,322 b, and 322 c is shown in FIG. 13. The probe 300 has a base 310 witha top 312, a bottom 314, a forward end 316, and a rear end 318. The base310 is typically made of rigid opaque material. However, it will beunderstood that the base 310 may be made of other materials which may berigid, resilient, opaque, or transparent, for example. A cross-sectionalview of the chamber 322 of this embodiment is shown in FIG. 14. Forclarity in the perspective view of FIG. 13, a material 328 on whichmeasurements are to be taken is not shown placed adjacent the probe 300.However, the material 328 is shown in the cross section of FIG. 13. Anaperture 320 of any shape is formed in the base 310, similar to theapertures 120 and 220 described above. The aperture 320 forms theopening to a stabilizing segment 322 a of a three segment chamber 322. Alateral cross-section (not shown) of the stabilizing segment 322 a ofthe chamber 322 is typically the same shape as the aperture 320. Walls323 a of the stabilizing segment 322 a are generally perpendicular tothe aperture 320. A central axis 324 of the chamber 322 is defined by aline aligned perpendicular to the aperture 320 and extending generallythrough a central portion of the aperture 320 and the chamber 322.

A second, transitional segment 322 b of the chamber 322 is adjacent thestabilizing segment 322 a of the chamber 322. A top border 325 a isformed between the transitional segment 322 b and the stabilizingsegment 322 a of the chamber 322. The transitional segment 322 b sharesthe same central axis 324 as the stabilizing segment 322 a. Walls 323 bof the transitional segment 322 b are angled inwardly such that a bottomborder 325 b of the transitional segment 322 b is of smaller dimensionthan the top border 325 a of the transitional segment 322 b.

The bottom border 325 b of the transitional segment 322 b leads into amounting segment 322 c of the chamber 322. The mounting segment 322 cshares the same central axis 324 of the stabilizing and transitionalsegments 322 a and 322 b and is typically of smaller width than thestabilizing and transitional segments 322 a and 322 b. Walls 323 c ofthe mounting segment 322 c are generally parallel to the central axis324. Thus, any cross-section of the mounting segment 322 c cutperpendicular to the central axis 324 of the chamber 322 is typically ofapproximately the same shape as the bottom border 325 b of thetransitional segment 322 b of the chamber 322. The mounting segment 322c may extend through the bottom 314 of the base 310, as shown.Alternatively, the mounting segment 322 c may extend to just above thebottom 314 of the base 310, leaving a shell (not shown) of base 310material at the bottom 314 of the three segment chamber 322.

A photodetector 326 is placed within the mounting segment 322 c of thechamber 322, at the bottom 314 of the chamber 322 in the presentembodiment. A central portion of the photodetector 326 is aligned withthe central axis 324 of the chamber 322. The mounting segment 322 c ofthe chamber 322 is deep enough that the photodetector 326 does notpenetrate into the stabilizing segment 322 of the chamber 322. Thephotodetector 326 may be fixed within the chamber 322 according to anumber of different methods, including but not limited to adhesive, apress fit, or a clear epoxy resin which transmits light over a range ofwavelengths of interest. In this embodiment, the bottom 314 of thechamber 322 is made opaque via the press fit, paint, or tape, forexample. The photodetector 326 is electrically connected to a processor,similarly to the photodetectors 126 and 226 in the previous embodimentsof the probe of the present invention.

When a portion of an energy absorbing material 328 is placed over theprobe 300, as shown in the cross-section of FIG. 14, it may rest abovethe chamber 322. Additionally, the stabilizing segment 322 a of thechamber 322 is wide enough that easily compressible portions of thematerial 328 may enter into the stabilizing segment 322 a of the chamber322. The stabilizing segment 322 a of the chamber 322 is deep enoughthat the easily compressible portion of the material 328 which intrudesinto the stabilizing segment 322 a does not contact matter within thestabilizing segment 322 a which might cause compression of the material328, even when the material 328 is caused to move. The chamber 322shields the compressible material 328 from contact which might causecompression of the material 328 and thereby change the optical pathlength through the material 328.

An LED 330 is affixed to the material 328, opposite the aperture 320.The LED 330 is advantageously aligned along the central axis 324 tooptimize the amount of light incident directly through the material 328onto the photodetector 326. It will be understood that the positions ofthe photodetector 326 and the LED 330 could be interchanged as discussedin conjunction with FIG. 7. Additionally, a collimating lens assembly(not shown) could be added to the chamber 322 as discussed inconjunction with FIG. 8. The collimating lens assembly may be held inthe chamber 322 similarly to a light collecting lens 332 discussedbelow. Further, it will be understood that the LED 330 and thephotodetector 326 could be unaligned, as discussed in conjunction withFIG. 9.

As light from the LED 330 propagates through the material 328, it isscattered by the material 328 and is thus transmitted into the chamber322 over a broad range of angles. Thus, some of the light is caused tobe incident on the opaque walls 323 a, 323 b, and 323 c of the chamber322 and is absorbed. However, the advantageous alignment of thephotodetector 326 and the LED 330 along the central axis 324 of thechamber 322 causes a large percentage of the light to be incident on thesurface of the photodetector 326. Since the material 328 remainssubstantially uncompressed above and within the stabilizing segment 322a, the thickness through which the light travels, or the optical pathlength, is substantially stabilized. Thus, the signal-to-noise ratio ofthe measured signal is improved by the suppression of motion artifacts.Additionally helping to improve the signal to noise ratio of themeasured signal is the opaque bottom 314 of the mounting segment 322 cwhich shelters the photodetector 326 from ambient light.

In another embodiment of the probe 300 of the present invention, a lightcollecting lens 332 is added to the transitional segment 322 b of thechamber 322, as shown in a cross sectional view in FIG. 15. The lens 332is supported in the transitional segment 322 b and may be held in thetransitional segment 322 b by a number of means, including but notlimited to optical adhesive, a lens retaining ring, or a press fit. Thelens has a generally planar surface 332 a aligned with the top border325 a of the transitional segment 322 b of the chamber 322 and agenerally convex surface 325 b extending into the transitional segment322 b of the chamber 322. The stabilizing segment 322 a of the chamber322 is deep enough that the lens 332 does not contact the easilycompressible material 328 which rests above or has intruded into thechamber 322.

The lens 332 collects light which is incident on the planar surface 332a. Much of the light which is incident on this surface 332 a at angleswhich would have been absorbed by the walls 323 a, 323 b and 323 c ofthe chamber 322 if the lens 332 were not present is now directed towardthe photodetector 326. Thus, a greater percentage of the lighttransmitted through the material 328 is caused to be incident on thephotodetector 326, resulting in a stronger measured signal.

It will be understood that the walls 323 b of the transitional segment322 b in each of the above described embodiments need not be sloped toachieve transition from larger width in the stabilizing segment 322 a tosmaller width in the mounting segment 322 c. The walls 323 b of thetransitional segment 322 b could be aligned generally parallel to thecentral axis 324, arranged at a distance which would cause the width ofthe transitional segment 322 b to be less than the width of thestabilizing segment 322 a and greater than the width of the mountingsegment 322 c.

FIG. 16 shows a perspective view of another probe 400 of the presentinvention specifically designed for use with a digit, such as a fingeror a toe. For ease of illustration, the present example will pertain toa finger, though it will be understood that the present example couldequally well pertain to any digit. FIG. 17 illustrates a schematicfinger 428 comprising nail, skin, bone, tissue, muscle, blood, etc.Constituents in the finger's pad 404, such as fat and tissue, are easilycompressible with motion of a patient. Even slight motion of the finger428 can cause the thickness of constituents within the finger 428 tochange greatly, thereby causing large motion induced excursions to occurin a measured signal, often obscuring a desired portion of the measuredsignal from which information about the patient can be determined.

As depicted in FIG. 16, base 410 of the finger probe 400, called asaddle 410 in this embodiment, is generally semi-cylindrical andpreferably is made of a rigid or semi-rigid, opaque material such asblack plastic. It will be understood, however, that the saddle 410 maybe made of other materials, including those which are rigid, resilient,opaque, and transparent, for example. The saddle 410 has a top 412, abottom 414, a forward end 416, a rear end 418, a ridge 440, andsidewalls 450 which curve upwardly from the ridge 440 to form a U-shapein cross-section, as shown in FIG. 18.

As illustrated in FIGS. 16 and 18, an aperture 420 forms the entrance toa chamber 422, located between one-quarter to one-half of the length ofthe saddle 410 from the forward end 416 of the saddle 410, as shown inthe longitudinal cross-section of FIG. 19. The aperture 420 can be ofany shape, including but not limited to circular, square, or triangular.The aperture 420 is the entrance to a chamber 422, as describedpreviously in conjunction with other embodiments 100, 200, and 300 ofthe probe of the present invention. The chamber 422 may also be of anyshape, including but not limited to circular, square, or triangular incross-section.

The chamber 422 may have one or more segments, as described previously.Although the chamber 422 shown in this embodiment is a three segmentchamber 422, having a stabilizing segment 422 a, a sloped-walltransitional segment 422 b, and a mounting segment 422 c aligned on acommon central axis 424, it will be understood that any chamber 422which protects from compression, a compressible portion of the finger428 through which light energy passes during absorption measurements, isa viable alternative. It will further be understood that a shell (notshown) of saddle 410 material could cover the bottom 414 of the chamber422, as described previously with respect to the embodiment of the probeshown in FIG. 5.

A photodetector 426 is placed within the chamber 422, typically at thebottom 414 of the mounting segment 422 c of the chamber 422. Thephotodetector 426 may be in place by adhesive, a press fit, or a clearepoxy resin which transmits light over a range of wavelengths ofinterest, for example. Typically, the bottom 414 of the chamber 422 ismade opaque via tape or paint, for example, such that ambient light doesnot affect the photodetector 426.

The finger 428 is placed on the saddle 410, the finger pad 404 directlyadjacent the aperture 420 and chamber 422. Additionally, the finger pad404 may rest above the chamber 422. The aperture 420 and stabilizingsegment 422 a of the chamber 422 are wide enough that any easilycompressible portion of the finger 428, such as a portion of the fingerpad 404, may intrude into the chamber 422. The stabilizing segment 422 aof the chamber 422 is deep enough that any portion of the finger 428which does penetrate into the stabilizing segment 422 a does not contactany matter within the stabilizing segment 422 a which might causecompression of the finger 428, even when the finger 428 is caused tomove.

An LED 430 is affixed to the finger 428, generally opposite the aperture420. The LED 430 is typically attached to the finger 428 via adhesive,such as medical tape. The LED 430 is advantageously aligned along thecentral axis 424 to optimize the amount of light transmitted directlythrough the finger 428 onto the photodetector 426. However, it will beunderstood that the positions of the photodetector 426 and the LED 430could be interchanged as discussed in conjunction with FIG. 7.Additionally, a collimating lens assembly (not shown) could be added tothe chamber 422 as discussed in conjunction with FIG. 8. The collimatinglens assembly may be held in the chamber 422 similarly to a lightcollecting lens 432 discussed below. Further, it will be understood thatthe LED 430 and the photodetector 426 could be unaligned, as discussedin conjunction with FIG. 9.

The LED 430 emits a light energy signal which propagates through thefinger 428 and is transmitted into the chamber 422. The chamber 422shields from compression the portion of the finger 428 through whichlight energy passes. Thus, the optical path length of the light throughthe finger 428 is substantially stabilized and motion artifacts aresubstantially reduced in the measured signal. It will be understood thata single segment chamber as described in conjunction with FIGS. 3through 9 or a two segment chamber as described in conjunction withFIGS. 10 through 12 could equally well be used in the finger probe 400of the present invention to shield the compressible portion of thefinger 428 from compression and thereby reduce motion artifacts.

FIGS. 16, 18, and 19 illustrate a perspective view, a frontalcross-sectional view, and a longitudinal cross-sectional view,respectively, of one embodiment of the finger probe 400. The curvatureof the saddle 410 is correlated to the average curvature of the finger428 such that the sidewalls 450 form a semi-circular splint-type supportfor the finger 428. The saddle 410 is approximately 25 mm long betweenthe forward end 416 and the rear end 418, such that a portion of thefinger 428 between its tip 406 and approximately its first knuckle 408(shown in FIG. 17) fits between the front 416 and the rear 418 ends ofthe probe 400. The curvature of the saddle 410 is generally defined by aline 460 (shown in FIG. 18) which is tangent to a sidewall 450 at anangle between 30□ and 5□ from horizontal.

The placement of the aperture 420 at a point between one-third andone-half of the length of the saddle 410, causes the thickest section ofthe compressible portion of the finger 428, or the finger pad 404, torest above and within the chamber 422. Thus, the portion of the finger428 with the greatest amount of compressible material is safeguardedfrom compression by the chamber 422.

In the embodiment of the finger probe 400 shown in FIGS. 16, 18, 19, and20, the aperture 420 is generally circular and the chamber 422 has threesegments 422 a, 422 b, and 422 c, as shown in the cross-sectional viewof FIG. 18. Advantageously employed dimensions for the finger probe 400illustrated in FIGS. 16, 18, 19, and 20 include the stabilizing segment422 a of the chamber 422 being generally cylindrical and having adiameter of approximately seven millimeters. Additionally, thestabilizing segment 422 a of the chamber 422 is deep enough that anyportion of the finger 428 which penetrates into the chamber remainssubstantially free of perturbation, even when the finger 428 moves. Anadvantageous depth for the stabilizing segment 422 a is thusapproximately two millimeters deep. The mounting segment 422 c of thechamber 422 is also cylindrical, having a diameter of approximately fivemillimeters. The transitional segment 422 b of the chamber 422 is ofvarying diameter, having sloped walls 423 b, such that a top border 425a is approximately seven millimeters in diameter and a bottom border 425b is approximately five millimeters in diameter. A detector 426 havingup to a 5 millimeter diameter is positioned in the bottom 416 of themounting segment 422 c of the chamber 422.

In another embodiment of the finger probe 400, a light collecting lens432 may be added to the finger probe 400 of the present invention, asshown in FIG. 20. The saddle 410 and the chamber 422 function asdiscussed above. The lens 432 functions as described above inconjunction with FIGS. 6, 12, and 15 to collect light incident on thelens 432 which would be absorbed by the walls 423 a, 423 b and 423 c ofthe chamber 422 if the lens 432 were not present. Thus, a greaterpercentage of the light transmitted through the finger 428 is directedonto the photodetector 426, resulting in a stronger measured signal.

Other embodiments of the probe of the present invention may bespecifically designed and manufactured for use with an earlobe or otherthin section of the body, such as a nostril or a lip, using theprinciples described herein. Also, embodiments of the probe of thepresent invention utilizing the properties of attenuation as energy isreflected from a medium, rather than transmitted through a medium, maybe made using similar principles.

A probe 700 specifically designed to measure reflected energy is shownin cross-section in FIG. 21. A base 710 is placed adjacent a material728 on which reflectance measurements are to be made. A photodetector726 and an LED 730 are located within the base 710. In the embodimentshown in FIG. 21, the photodetector 726 is positioned within a chamber722 x and the LED 730 is positioned within a chamber 722 y. Althoughsingle segment chambers 722 x and 722 y are illustrated, the chambers722 x and 722 y may be of any suitable shape and size. The chambers 722x and 722 y function to stabilize the optical path length, as discussedpreviously, by shielding from compression any compressible portion of amaterial which rests above or intrudes into the chambers 722 x and 722y.

A light collecting lens (not shown) may be added to the chamber 722 xhaving the photodetector 726 within it, as discussed previously inconjunction with FIGS. 6, 12 and 15. Additionally, a collimating lensassembly (not shown) may be added to the chamber 722 y having the LED730 in it, as discussed previously in conjunction with FIG. 8. Thechambers 722 x and 722 y may be formed with or without a shell (notshown) of base 710 material, as discussed previously in conjunction withFIG. 5.

It will be understood that in other embodiments (not shown) of thereflectance probe 700, the photodetector 726 could protrude from thebase 710 and the LED 730 be located within a chamber 722 y or the LED730 could be protrude from the base 710 and the photodetector 726 couldbe located within a chamber 722 x. Additionally, the photodetector 726and the LED 730 could be located within a single chamber 722. In anyembodiment the chamber(s) 722 may have any number of segments of anysuitable shape.

The type of probe 700 which relies on reflection may be advantageouslyutilized on materials where a photodetector 726 and an LED 730 cannot beplaced on opposite sides of the material 728, such as with the forehead.However, a reflectance probe 700 can be used anywhere a non-invasivemeasurement needs to be taken, such as a lip, an earlobe, or a finger,for example.

FIG. 22 shows a cross-sectional view of another probe 800 of the presentinvention wherein two bases 810 x and 810 y are placed adjacent to amaterial 828 on which measurements are to be made. The bases 810 x and810 y are located on opposite sides of the material 828. A photodetector826 is placed in a chamber 822 x in the base 810 x. An LED 830 is placedin a chamber 822 y in the base 810 y. The photodetector 826 and the LED830 are aligned substantially along a central axis 824. Although twosegment chambers 822 x and 822 y are illustrated, the chambers 822 x and822 y may be of any suitable shape and size. Independent of which shapeof chamber is utilized, the chambers 822 x and 822 y function tostabilize the optical path length and thereby reduce the effects ofmotion artifacts on the measured signals.

As discussed previously, the probe 800 may be modified slightly with alight collecting lens (not shown) added to the chamber 822 x with thephotodetector 826 in it. A collimating lens assembly (not shown) may beadded to the chamber 822 y with the LED 830 in it. Additionally, thechambers 822 x and 822 y may be formed with or without a shell (notshown) of base 810 x and 810 y material. The probe 800 is particularlyadvantageous when a material 828 is compressible on more than one sidesince each chamber 822 x and 822 y supports and shields from compressionany compressible portion of a material 828 which rests above or intrudesinto the chambers 822 x and 822 y, respectively.

FIG. 23 shows a cross-sectional view of another probe 900 of the presentinvention wherein a chamber 922 having walls 923 is formed toconcentrate, or “funnel,” energy onto the surface of a photodetector926. An aperture 920 is formed in a base 910, the aperture 920 leadingto a generally cone-shaped chamber 922. The base 910 is placed adjacenta material 928 on which measurements are to be made, the chamber 922being placed directly adjacent any easily compressible portion of thematerial 928. The photodetector 926 is placed within the chamber 922,typically at the bottom of the chamber 928. A light emitting diode 930is placed on the material 928, generally opposite and aligned with thephotodetector 926.

As discussed previously, a portion of the material 928 is supported bythe area surrounding the aperture 920. Additionally, the aperture 920and chamber 922 are wide enough that any easily compressible portion ofthe material 928 may intrude into the chamber 922 without beingcompressed, thereby shielding this portion of the material 928 fromcompression, even during motion of the material 928. This substantiallystabilizes the optical path length and improves the signal to noiseratio of the signal measured at the photodetector 926.

Further improving the signal to noise ratio of measurements made withthe probe 900, reflective material, such as a highly reflective metal,covers the walls 923 of the chamber 922. This causes light scattered bythe material 928 and made incident on the walls of the chamber 922 to bereflected. The cone shape causes the light to be concentrated generallyon the photodetector 926.

Depending upon the shape of the photodetector 926, the chamber 922 maybe advantageously contoured to maximize the funneling of light onto thephotodetector 926. If the photodetector 926 is flat, the chamber is mostadvantageously shaped having a generally hyperbolic cross-section.However, if the photodetector 926 is spherical or slightly curved, as isoften the case due to manufacturing processes, the chamber is mostadvantageously shaped having a cone-shaped cross-section with uncurvedwalls 923.

As discussed previously in conjunction with other embodiments of theprobe of the present invention, the probe 900 may be modified to includea light collecting lens (not shown). Alternatively, an LED 930 could beplaced within the chamber 922 instead of the photodetector 926. With theLED in the chamber 922, a collimating lens assembly (not shown) could beplaced within the chamber 922. Two bases 910 with two generallycone-shaped chambers could be utilized on one or either side of amaterial 928. A single base 910 with two generally cone-shaped chambers922 located side by side could also be used for reflective measurements.Additionally, the photodetector 926 and the LED 930 need not be alignedalong the central axis 924.

FIG. 24 depicts one embodiment of a probe constructed in accordance withthe present invention coupled to an oximeter. The oximeter could be anyoximeter known in the art which utilizes light attenuation measurements.A block diagram of one possible oximeter is depicted in FIG. 24. Theoximeter shown in FIG. 24 is a pulse oximeter wherein the finger probe400 is employed and two measured signals at different wavelengths, oneof which is typically red and the other of which is typically infrared,are alternately passed through the finger 428. Signals measured at thephotodetector 426 are then processed to determine the amount of oxygenavailable to the body. This is evaluated by finding the saturation ofoxygenated hemoglobin in blood comprising both oxygenated anddeoxygenated hemoglobin.

Two LEDs 430 a and 430 b, one LED 430 a emitting red wavelengths andanother LED 430 b emitting infrared wavelengths, are placed adjacent thefinger 428. The finger probe 400 is placed underneath the finger 428,the aperture 420 and chamber 422 located directly adjacent the fingerpad 404. The photodetector 426 in the bottom 414 of the chamber 422 isconnected to a single channel of common processing circuitry includingan amplifier 530 which is in turn connected to a band pass filter 540.The band pass filter 540 passes signal into a synchronized demodulator550 which has a plurality of output channels. One output channel is forsignals corresponding to visible wavelengths and another output channelis for signals corresponding to infrared wavelengths.

The output channels of the synchronized demodulator 550 for signalscorresponding to both the visible and infrared wavelengths are eachconnected to separate paths, each path comprising further processingcircuitry. Each path includes a DC offset removal element 560 and 562,such as a differential amplifier, a programmable gain amplifier 570 and572 and a low pass filter 580 and 582. The output of each low passfilter 580 and 582 is amplified in a second programmable gain amplifier590 and 592 and then input to a multiplexer 600.

The multiplexer 600 is connected to an analog-to-digital converter 610which is in turn connected to a microprocessor 620. Control linesbetween the microprocessor 620 and the multiplexer 600, themicroprocessor 620 and the analog-to-digital converter 610, and themicroprocessor 620 and each programmable gain amplifier 570, 572, 590,and 592 are formed. The microprocessor 620 has additional control lines,one of which leads to a display 630 and the other of which leads to anLED driver 640 situated in a feedback loop with the two LEDs 430 a and430 b.

Each of the LEDs 430 a and 430 b alternately emits energy which isabsorbed by the finger 428 and received by the photodetector 426. Thephotodetector 426 produces an electrical signal which corresponds to theintensity of the light energy striking the photodetector 426 surface.The amplifier 530 amplifies this electrical signal for ease ofprocessing. The band pass filter 540 then removes unwanted high and lowfrequencies. The synchronized demodulator 550 separates the electricalsignal into electrical signals corresponding to the red and infraredlight energy components. A predetermined reference voltage, V_(ref), issubtracted by the DC offset removal element 560 and 562 from each of theseparate signals to remove substantially constant absorption whichcorresponds to absorption when there are no motion artifacts. Then thefirst programmable gain amplifiers 570 and 572 amplify each signal forease of manipulation. The low pass filters 580 and 582 integrate eachsignal to remove unwanted high frequency components and the secondprogrammable gain amplifiers 590 and 592 amplify each signal for furtherease of processing.

The multiplexer 600 acts as an analog switch between the electricalsignals corresponding to the red and the infrared light energy, allowingfirst a signal corresponding to the red light to enter theanalog-to-digital convertor 610 and then a signal corresponding to theinfrared light to enter the analog-to-digital convertor 610. Thiseliminates the need for multiple analog-to-digital convertors 610. Theanalog-to-digital convertor 610 inputs the data into the microprocessor620 for calculation of the saturation of oxygen according to knownmethods, such as those described in U.S. patent application Ser. No.07/666,060 filed Mar. 7, 1991, and abandoned in favor of continuationU.S. patent application Ser. No. 08/249,690, entitled “SIGNAL PROCESSINGAPPARATUS AND METHOD,” filed May 26, 1994, both assigned to MASIMOCORPORATION, the same assignee as the present patent, and incorporatedherein by reference. U.S. patent application Ser. No. 08/320,154,entitled Signal Processing Apparatus, filed on Oct. 7, 1994 is alsoincorporated by reference herein. The microprocessor 620 centrallycontrols the multiplexer 600, the analog-to-digital convertor 610, andthe first and second programmable gain amplifiers 570, 590, 572, and 592for both the red and the infrared channels. Additionally, themicroprocessor 620 controls the intensity of the LEDs 430 a and 430 bthrough the LED driver 640 in a servo loop to keep the average intensityreceived at the photodetector 426 within an appropriate range.

As explained above, the probe of the present invention could be usedwith a variety of oximeter systems. A recent embodiment of an oximeterby the assignee of the present application is described in detail inU.S. patent application Ser. No. 08/320,154, entitled “Signal ProcessingApparatus,” and filed Oct. 7, 1994, which patent application is alsoincorporated herein by reference.

FIGS. 25-28 depict alternative embodiments of the present inventionwherein an improved signal to noise ratio is observed in the receivedsignal due to optical scattering effects. A probe 1000, shown incross-section in FIG. 25, includes a base 1010, having a top 1012, abottom 1014, and a forward and a rear end (not shown in FIG. 25). Thebase 1010 is preferably rigid and opaque to the wavelengths used in theprobe 1000. An aperture 1020 is formed in the top 1012 of the base 1010.The aperture 1020 may be cylindrical (as shown in FIG. 25), conical,rectangular, or other shapes as called for by the specific application.The depth of the aperture 1020 may, for example, range from 0.5 mm to 10mm, and is preferably in the range of 2-4 mm in depth in one embodiment,and more preferably in the range of 3-4 mm. Furthermore, the diameter ofthe aperture 1020 may range from 3 mm to 20 mm, as called for by thespecific application. It has been found by the inventors that anaperture less than 0.5 mm in diameter does not obtain the benefits ofthe present invention.

A light source 1030 (e.g., one or more light emitting diodes) is affixedadjacent to material 1028 (e.g., an earlobe, finger, or other fleshymaterial), aligned along a central axis 1024 which passes substantiallythrough the center of a photodetector 1026. The aperture 1020 is filledwholly, or in part, by a scattering medium 1040, which may, for example,comprise 2.2 pound polyurethane reticulated foam (although conformableplastic or scattering gels may also be employed). In general, thescattering medium may comprise one of a number of fixotropic materials(i.e., materials having two or more mixed materials which are conduciveto scattering). Ideally, the scattering medium 1040 scatters but doesnot significantly absorb optical radiation at the operational red (e.g.,660 nm) and infrared (e.g., 940 nm) wavelengths for the oximeter. Inother words, the material is clear to optical absorption, but stillscatters light.

In operation, the light source 1030 (e.g., two LEDs in the presentembodiment) emits optical radiation (e.g., in the red or infra-redspectrum range) which passes through the material under test 1028. Theoptical radiation is received by the photodetector 1026 after passingthrough the scattering medium 1040. The received optical radiation isscattered by the scattering medium 1040.

The scattering of the optical radiation within the scattering medium1040 has been found to increase the signal-to-noise ratio of thereceived signal. It is believed that the signal-to-noise ratio isimproved because there appears to be a reduced effect on the signal fromany particular local region of the material 1028 (e.g., flesh). That is,by scattering the signal either prior to or posterior to the materialinterface, the signal is effectively spread over a larger area of thematerial 1028. Thus, perturbations of a locality within the area ofexposure will have less effect with a scattered beam over a large areathan with a more concentrated signal passing through that same locality.In this way, the effect of perturbations on the average signal isreduced. Also, the foam and plastic cover reduce optical decoupling andgeometric variation in the optical light path during motion.

The scattering medium 1040 or plastic cover should be soft (i.e., highlycompressible) so that the material 1028 does not significantly compresswhen the material 1028 presses against the scattering medium 1040.Compression of the scattering medium 1040 does not significantly alterthe amplitude of the measured signal since the scattering medium is nothighly absorptive of the optical radiation. Although conformable plasticcovers may be used, reticulated foams provide improved optical couplingwith flesh. This is because the reticulated foam provides contact inspots rather than across large areas of the flesh. If contact is madeacross large areas of flesh, microscopic droplets of perspiration or oilcan form a layer between the flesh and the scattering medium 1040. Thislayer creates an impedance mismatch interface which is absorptive of theoptical radiation. Of course, gels may also be used in accordance withthe present invention. Such gels should not contain significant amountsof metal salts or silica because these materials absorb light.

The teachings of the present invention depart from conventional methodsof improving optical signal-to-noise ratios. Commonly, lens assemblieswhich focus optical radiation are used to improve the signal-to-noiseratios of optical signals. However, oximetry by means of transmission orreflection is a non-imaging method of optical detection. Thus, the formof the image is not important for detection purposes. For this reason,scattering may be used as a method of improving optical signal quality;whereas, since scattering was thought to degrade signal-to-noise ratiosof optical signals, previous methods have not employed opticalscattering techniques.

FIGS. 26 and 27 depict further alternative embodiments of the presentinvention wherein optical scattering is provided prior to the fleshinterface, and both prior and posterior to the flesh interface,respectively. In FIG. 26, an oximetry probe 1045 further has atransmission assembly 1050 which secures the LED 1030 in place within abacking 1055. A scattering medium 1060, having a face 1063, isinterposed between the LED 1030 and the material 1028. In the embodimentdepicted in FIG. 26, the scattering medium 1060 does not contact the LED1030; however, it should be understood that the scattering medium 1060may contact one or both of the LED 1030 and the material 1028.

The scattering medium 1060 diffuses the optical radiation emitted by theLED 1030 over a wider area. Thus, the LED 1030, which is essentially apoint source, is transformed into an evenly distributed source of lightover the entire area of the face 1063 of the scattering medium 1060. Thediffusion of the light over a wider area provides an improvedsignal-to-noise ratio.

As seen in FIGS. 26-28, the light is scattered. This is represented bythe energy intensity contours rather than light path indicators. Asrecognized by the present inventors, the particular light path is notsignificant. The important aspect is the intensity of the light and thefield of view of the photodetector and the light source. This will beexplained further in connection with the embodiment of FIG. 28 utilizingan immersion lens.

The operation of a probe 1065 shown in FIG. 27 is essentially the sameas that of the probe 1045, with the exception that the scattering medium1040 is provided within the aperture 1020. It has been found that byproviding a scattering medium on both sides of the material 1028, animproved signal-to-noise ratio is observed over the probes having ascattering medium on only one side of the material 1028.

FIG. 28 depicts a preferred embodiment of a probe 1070 in accordancewith the present invention. As depicted in FIG. 28, the probe 1070comprises a transmission assembly 1072, having a light source 1074, animmersion lens 1076, scattering medium 1078, a chamber 1080 defining anaperture 1082 along a support surface 1083 of the transmission assembly.A detector assembly 1084 is similarly configured with a support surface1085, a chamber 1086 defining an aperture 1088 along the support surface1085, a photodetector 1090, an immersion lens 1092 and scattering medium1094. FIG. 28 further depicts a test material 2000 such a human tissue(e.g., a finger or earlobe) interposed between the light source assembly1072 and the detector assembly 1084.

Several advantages are obtained from the particular configuration shownin FIG. 28. First, it should be understood that an economical way tofabricate the light source in the photodetector is to utilize smallsemiconductor LEDs and photodetectors. Such devices are very small, andtherefore, have a very small field of view. The inventors haverecognized that it is advantageous to improve the field of view of thephotodetector and the LED because the surface of the tissue material2000 at the aperture of the support surfaces is large compared to thesurface of the semiconductor photodetector and LED. Thus, withoutenlarging the field of view of the photodetector and/or LED, much of thetissue material interface at the apertures is not utilized. As explainedabove, scattering of the light improves the received signal quality. Animmersion lens for the photodetector and/or LED increases the field ofview of the semiconductor photodetector and LEDs such that a substantialportion of the tissue material covering the apertures is within thefield of view of the photodetector and/or LED.

Because imaging optics are not required due to the advantages ofscattering, a significantly advantageous configuration is to utilizeepoxy placed directly over the photodetector and/or over the LED in theform of a partial sphere which performs suitably as an immersion lens inthe present embodiment. In one embodiment, the index of refraction ofthe epoxy is advantageously 1.56 in the present embodiment. The epoxyalso acts to protect the photodetector and/or LED. The immersion lenscan be formed by placing a bump of epoxy over the photodetector and theLED.

The immersion lens formed by a bump of epoxy over the photodetectorand/or LED expands the field of view for the photodetector and LED inorder to disperse the transmitted light energy over the tissue surfacearea at the apertures which is large relative to the surface of theoptical elements. This assists in minimizing the effects of therelatively small optical details of the test materials (e.g., pores,fingerprint lines, sweat glands).

In the advantageous embodiment of FIG. 28, the scattering material 1080,1086 is also placed in the chambers 1080, 1086 in order to enhancescattering of the light as explained above.

The cone shaped chambers 1080, 1086 depicted in FIG. 28 are alsoadvantageous when the walls of the chambers are coated with a highlyreflective material which does not absorb the light from the LED. Thecone shape assists in reflecting the light energy away from the LED andtoward the photodetector. All of these elements in combination form aparticularly advantageous probe which can maximize the signal-to-noiseratio of the probe and minimize the effects of motion artifact on thereceived signal.

It should be understood that in alternative embodiments of the probe1070 depicted in FIG. 28, elements could be removed and still obtainsignificant benefit. For instance, the detector assembly 1084 couldremain the same with the light source assembly 1072 simply becoming anLED with no support surface and no chamber. Alternatively, thescattering media 1078, 1086 could be removed from either the chamber1080 in the light source assembly 1072 or the chamber 1086 in thedetector assembly 1082.

The light collecting lens, or other optical elements, could also beadded to the chamber in any optical probe of the present invention todirect light onto the photodetector. However, the immersion lensprovides better performance. The location of the photodetector and theLED may be interchanged in any of the above described probes. The bottomof any chamber formed in a base of an optical probe of the presentinvention can remain exposed, be covered by a material such as opaquetape, or be covered by a shell of base material without affecting thereduction of motion artifacts brought about by the chamber.Additionally, reflective measurements could be made with the probes ofthe present invention by mounting both the photodetector and LED on thebase of the probe. Also, a plurality of LEDs or photodetectors could bemounted in the chamber or affixed to the material such that more thanone signal may be measured at a time. Furthermore, any material having achamber, with a detector or an LED mounted within the chamber, willreduce the effects of motion artifacts in non-invasive absorption (orreflection) measurements, according to the present invention.

FIGS. 29A-29B depict one embodiment of a disposable, optical probe 2002,and the attachment of the optical probe 2002 on the fingertip 2050 of anadult patient. As shown in FIGS. 29A-B, the disposable optical probe2002 is designed to fit comfortably onto a patient's fingertip.Advantageously, the optical probe 2002 is also configured to provide oneor more of the following features: (i) minimization of undesirablemovement with respect to the tissue under test (e.g., due to motion bythe patient or contact of the probe 2002 with an object or surface);(ii) minimization or prevention of “light piping” (transmission)directly from the light source (e.g., light emitting diode) to thedetector (e.g., photodetector), (iii) minimization of the detector andLED decoupling from the test site during motion, and (iv) the low noisechamber configuration described above.

As illustrated in FIG. 29A, the probe 2002 includes a central portion2004, a pair of adhesive flanges 2005 extending from the central portion2004, a connector portion 2010 situated between the flanges 2005, and apair of smaller adhesive flaps 2015 extending from the central portion2004 on the end of the optical probe 2002 opposite from the connector2010. The probe 2002 further includes a connection aperture 2012 formedin the connector tab 2010, an emitter aperture 2020 with an emitter(e.g., a light-emitting diode) positioned within the central portion2004 close to the connector portion 2010. A flex pocket 2025 is locatedwithin the central portion between the emitter aperture 2020 and adetector aperture 2030 which allows light to pass through the detectoraperture 2030 to a detector assembly 2035. An adult fingertip 2050 isshown in phantom in FIG. 29A to illustrate the position at which thefingertip 2050 would be placed when the probe 2002 is to be fastenedonto the fingertip 2050 for use.

Although not depicted specifically in FIGS. 29A-29B, the probe 2002 isfabricated from multiple layers, including a flex circuit layer, aMYLAR™ layer, a face stock tape layer, and other tape layers, depictedfurther in FIGS. 31-39.

FIG. 29B illustrates the probe 2002 fastened onto the fingertip 2050. Asshown in FIG. 29B, the probe 2002 folds at the location of the flexpocket 2025 over the fingertip 2050 such that the flex pocket 2025aligns with the very end of the fingertip and such that adhesive flaps2005 fold downward (in the illustration of FIG. 29B) to wrap around thefingertip 2050 while the adhesive flaps 2015 fold upward (in theillustration of FIG. 29B) about a portion of the circumference of thefingertip 2050 to provide support. As shown in FIG. 29B, when the probe2002 is folded about the fingertip 2050, the emitter located within theprobe is spaced opposite the detector assembly 2035 such that light fromthe emitter passes through the emitter aperture 2020, through the finger2050 and is incident upon the detector assembly 2035 through thedetector aperture 2030.

Advantageously, when the probe 2002 is attached to the finger, the flexpocket 2025 is aligned at the tip of the finger 2050 so as to providealignment of the probe 2002 on the fingertip 2050. The flex pocket 2025also provides a highly flexible portion, thus providing for reducedmovement of the detector and LED assembly with respect to the finger2050 if the fingertip comes into contact with another object. Thisprovides a more stable probe with increased motion resistance. In otherwords, the flex pocket also assists in minimizing perturbations in thedetected signal due to movement of the detector and emitter with respectto the test tissue (e.g., the finger). Furthermore, the flex pocket 2025reduces light piping since light is diverted around the circumference ofthe pocket.

In one embodiment, the flex pocket 2025 is formed to include an aircushion or other cushion material to further absorb contact of the probe2002 with objects. In this manner, jarring of the probe 2002 in theevent the fingertip 2050 moves slightly or in the event of contact ofthe probe to another surface is minimized.

The probe 2002 includes an internal flex circuit 2051 which acts as aspring-like shock absorber for the disposable probe. The flex circuit2051 also assists in reducing shifting between the emitter 2021 and thedetector assembly 2035 due to contact or motion by the patient. Thus,the internal flex circuit 2051, together with the flex pocket 2025 actto minimize the decoupling of the detector assembly.

FIG. 29B depicts a receiving connector portion 2060 which engages withcontacts 2052 on the connector 2010 to provide an electrical connectionbetween the optical probe 2002 and digital signal processing circuitry(not shown in FIG. 29C). The digital signal processing circuitry may beused to analyze the output of the detector within the assembly 2035. Inone advantageous embodiment, the aperture 2012 catches onto a tab (notshown) within the connector 2060 to firmly secure the connector 2060with the optical probe 2002. Once the optical probe 2002 is securelyfastened to the fingertip 2050 and the connector provides an electricalconnection between the optical probe 2002 and digital signal processingcircuitry, signals are detected from the detector 2035 and transmittedto the processing circuitry via the connector 2060. Further details ofthe receiving connector portion 2060 are described in a patentapplication entitled “Patient Cable Connector” filed on the same date asthe present application and assigned to the assignee of the presentapplication, which application is incorporated herein by reference as iffully set forth.

FIG. 30 is a flow chart which illustrates the general steps inaccordance with the present invention to manufacture a first embodimentof the disposable, optical probe 2002 depicted in FIGS. 29A-29C. A flexcircuit is formed on a flex circuit panel as represented by an activityblock 3005. In one advantageous embodiment, the flex circuit panelcomprises a copper/MYLAR™ or copper/CAPTON™ laminant, or, alternatively,is formed by depositing a conductive ink on MYLAR™. For example, FIG. 31depicts three etched flex circuits on a flexible circuit panel material.The flex circuits have been formed by etching in one preferredembodiment, and are comprised of one-ounce copper (approximately 1.3mils) over 1 mil of MYLAR™ or CAPTON™.

After the flex circuit has been etched in an appropriate copper coatedMYLAR™ substrate material, conductive pressure sensitive adhesive (PSA)2102 is applied to the end of the flex circuits where the detector willbe placed (hereinafter, the “detector end”), as depicted in FIG. 31.After the conductive PSA (made by 3M in the present embodiment, part No.9703) is applied, a detector component window 2104 is cut through theconductive PSA 2102 and the flex circuit MYLAR™ base. An emittercomponent window 2106 is also cut through the flex circuit MYLAR™ base.A flex pocket hole 2108 is also cut through the flexible circuit MYLAR™base. Next, detector shields 2110 are placed on the PSA at the end ofthe detector end of the flex circuit, as depicted in FIG. 31A.

In one embodiment, the detector shields are etched copper shields madeof copper sheet. A grating 2111, which is about 80% open, is etchedthrough the shields to allow light from the light source (e.g., LED) totransmit through the shield to a detector. The resultant shield has aframe of approximately 4 mils thickness and a grating of approximately 2mils thickness. The shields provide a Faraday Shield for the detector.

The diffraction grating aligns with the detector component window 2104in the flex circuit and, when the probe is assembled, with the detectoraperture 2030 (FIG. 29A). The conductive PSA 2102 makes electricalconnection between a flex circuit ground trace 2112 and the detectorshield 2110 to connect the detector shield 2110 to ground.

In one preferred embodiment, low temperature solder paste is dispensedon contacts 2114, 2115, for the detector connections (FIG. 31B), oncontacts 2116, 2117 for the emitter connections and on resistor pad 2118for an identifying resistor. The emitter (LED) 2021, a detector 2120 anda resistor 2122 are placed and soldered in the appropriate positions onthe flex circuits as depicted in FIG. 31B, and represented in anactivity block 3010 (FIG. 30). The solder operation is preferablyperformed through a direct heat reflow of the low temperature solder.The emitter 2021 and detector 2120 are placed such that the transmissionand detection field of view are through the detector and emitter windows2104 and 2106 (FIG. 31).

In one embodiment, the resistor 2122 advantageously is connected to theground trace on one end and a resistor signal trace 2113 at the otherend. In another embodiment, the resistor 2122 is connected in parallelwith the emitter 2021. The advantages of this parallel connection areexplained in detail in copending application Ser. No. 08/478,493entitled Manual and Automatic Probe Calibration, which is incorporatedherein by reference as if fully set forth.

In one embodiment, the resistor 2122 provides a company identifier. Inother words, the resistor 2122 can provide a value that specificallyidentifies that the probe is made by or for a particular patientmonitoring company. As explained in copending application Ser. No.08/478,493 the resistor can be read by lowering the voltage across theLED to a point where the LED is effectively off, thereby removing theLED from the circuit as a current draw.

As mentioned above, and as seen in FIG. 31B, the flex circuit has theaperture 2108 which is the aperture in the flex circuit forming aportion of the flex pocket 2025 of the probe 2002. In addition to theadvantages of the high flexibility, this aperture 2108 through the flexcircuit prevents a direct line of transmission between the emitter 2021and the detector 2120. In other words, in use, light from the emitter2021 which reaches the detector 2130 should pass through the mediumunder test (e.g., the finger or other tissue). Direct transmission ofstray light from the emitter directly to the detector 2120 along a lightconductive surface can cause erroneous readings, especially duringmotion. This direct transmission of light between the transmitter anddetector is referred to herein as “light piping.” That is, if the probebetween the emitter 2021 and the detector 2120 has optical transmissionproperties, due to the construction or the material of the probe, straylight from the emitter may channel along the probe directly to thedetector, without passing through the tissue material under test. Lightpiping is a heretofore unrecognized cause of noise and invalid signalsfrom such optical probes. The aperture 2108 minimizes or prevents this“light piping” by preventing or minimizing a direct line of transmissionfrom the emitter 2021 to the detector 2120 along the flexible circuit.Thus, the aperture 2108 provides benefits in the present invention ofproviding a highly flexible portion of the flex circuit, which reducesdecoupling of the LED 2021 and the detector 2120 during motion (due, forexample, to tapping on the finger tip), and preventing light pipingbetween the emitter and the detector.

Once the appropriate circuit elements are placed and soldered onto theflex circuit, a flex circuit shield 2130, as depicted in FIG. 32A, isattached to the flex circuit panel as represented in an activity block3015. The placement of the flex circuit shield 2130 with the flexcircuit is depicted in FIGS. 32A and 32B. The flex circuit shield 2130is advantageously constructed from MYLAR™ laminated with a thinconductive layer such as copper. In the present embodiment, thelaminated MYLAR™ is made by ACUTEK.

In the present embodiment, the flex circuit shield 2130 has an insulatorfilm 2132 depicted in double-cross hatching (made by Coating Sciences,part number P-341 in the present embodiment), a flex circuit shieldconductive PSA strip 2133 (made by 3M, part no. 9703 in the presentembodiment) and two non-conductive PSA strips 2134, 2135. As seen inFIG. 32A, the flex circuit shield 2130 has an emitter aperture 2136, twoflex pocket apertures 2137, and a detector aperture 2138.

When the flex circuit shield 2130 is applied to the flex circuit, theinsulator strip 2132 insulates the signal traces of the flex circuitfrom the metallization of the flex circuit shield 2130 to prevent shortcircuits. As further depicted in FIGS. 32A and 32B, when the flexcircuit shield 2130 is positioned such that the apertures align withcorresponding apertures on the flex circuit, the PSA strip 2135 providesbonding with the back of the flex circuit, the conductive PSA strip 2133provides for bonding of one tab of the detector shield 2110 with theflex circuit shield 2130. The conductive PSA strip 2133 also providesconnection of the flex circuit shield with the ground via the detectorshield tab.

With the flex circuit shield in position, the flex circuit assembly 2132(including the flex circuit, the emitter 2021, the detector 2120, theresistor 2122, and the shields 2110, 2130), are die-cut, as depicted inFIG. 33A. The flex circuit shield 2130, along with the detector shield2110, is folded over the flex circuit as represented in an activityblock 3020. The final flex circuit assembly 2051 is depicted in FIG.33B.

Once folded, the insulator film 2132 prevents contact from the flexcircuit traces to the metallization in the flex circuit shield 2130. ThePSA strip 2135 bonds the flex circuit shield to the signal circuit sideof the flex circuit. As depicted in FIG. 33B, the contact fingers 2052remain exposed.

As illustrated in FIG. 34, a base material 2140 also forms a layer ofthe probe 2002. In one embodiment, the base material comprises Avery3044 base material. Each side of the base material is coated with PSAadhesive (Coating Sciences, Inc., P-341 in the present embodiment). Theback side (in reference to the illustration of FIG. 34) of the basematerial 214 is provided with the thin release liner 2003 (see FIG. 29A,not shown in FIG. 34), preferably made from a paper release liner or thelike, as is well understood in the art.

In the present embodiment, the base material is transparent to thewavelength of the emitter 2021. The connector tab 2010 and an opticalcavity 2150, are placed onto a first adhesive side of the base material2140, as represented within an activity block 3025, and depicted in FIG.34. The connector tab 2010 is advantageously formed of ABS styrene, andhas the aperture 2012. The optical cavity 2150 may, for example, havethe configuration for its walls in the shape of any of theabove-disclosed bases (e.g., the bases 110, 1010, etc.) having a chamberformed therein. As depicted in FIG. 34, the optical cavity has arectangular receiving receptacle 2152 adapted to receive the detectorend of the completed flex circuit assemblies.

Additional detail of the optical cavity of the present embodiment of theprobe 2002 is depicted in FIG. 39A-39C. FIG. 39A depicts a perspectiveview of the optical cavity 2150 for the probe 2002. FIG. 39B depicts abottom view of the optical cavity 2150 and FIG. 39C depicts a crosssectional view along 39C-39C of FIG. 39A. The optical cavity 2150 ismade from styrene in one embodiment. In one preferred embodiment, theoptical cavity is coated with an optical coating that is opaque toambient light. This can be on the inside walls of the optical cavity orover the exterior walls of the optical cavity, or the entire opticalcavity can be coated. The opaque coating advantageously prevents orminimizes the transmission of ambient light from the surroundingenvironment which could be incident on the detector if the opticalcavity is not opaque to ambient light. As an alternative to an opaquecoating, the optical cavity can be made from a material that is opaqueto ambient light.

Advantageously, the optical cavity 2150 has a wedge shape ramp 2154 aspart of the rectangular receptacle 2152. As briefly mentioned above, therectangular receptacle 2152 is adapted to receive the detector end ofthe flex circuit 2051. The wedge shaped ramp 2154 of the optical cavity2150 provides a ramp for a smooth transition for the flex circuit 2051between the surface of the base material to the rectangular receptacletable 2152.

Further illustrated in FIG. 40A are two side walls 2156 that runs alongthe side border of the rectangular receptacle 2152 and an end wall 2157that runs between the two side walls 2156. These walls hold the flexcircuit 2051 in position such that the detector 2120 aligns properlywith an aperture 2158 in the optical cavity. Preferably, the flexcircuit fits snugly between the side walls 2156 and against the end wall2157.

In a preferred embodiment, the aperture 2158 has the configuration ofthe cavities describe above (e.g., cone-shaped, cylindrical in shape, orconical in shape, etc.).

Preferably, the PSA on the first adhesive side (FIG. 34) of the basematerial 2140 allows simple attachment of the optical cavity 2150 andthe connector tab 2010 through the application of pressure.

After the connector tab 2010 and the optical cavity 2150 have beenplaced on the base material 2140, the flex circuit assembly 2051 isplaced on top of the base material 2140, the connector tab 2010 and theoptical cavity 2150 as depicted in FIG. 35 on one end. The detector end2141 of the completed flex circuit assembly 2051 seats within therectangular receptacle 2152 of the optical cavity 2150, as depicted inFIG. 35. Mounting of the completed flex circuit assemblies 2051 isrepresented in an activity block 3030 (FIG. 30).

With the detector end 2141 of the flex circuit assembly 2051 seated inthe receptacle 2152 of the optical cavity 2150, the photodetectormounted to the flex circuit assembly 2151 is positioned to aligned withthe aperture 2158 of the optical cavity 2150. In one embodiment, a hole,corresponding to the emitter aperture 2020 and the detector aperture2030, is cut in the base material to correspond to the emitter 2021 andthe detector 2120. However, in the present embodiment, the base materialis transparent to the wavelength of the emitter 2021; therefore, holesare not provided through the base material 2140 for the detector andemitters.

As explained above in general, one of the advantages of the opticalcavity 2150 is that fleshy tissue can enter the cavity withoutsignificant perturbation in the area of the field of view of thedetector. Even if no hole is cut in the base material, if the basematerial chosen is very flexible, perturbation of the fleshy tissue inthe field of view of the detector 2100 will be minimal due to theoptical cavity aperture 2158, with the added benefit of not creatingoptical geometrical changes if the base material is not removed over thecavity.

A cover 2160 is placed over the optical cavity 2150 as represented in anactivity block 3035, and shown in FIG. 36. The cover is advantageously avacuum formed, cup-shaped cover. In the present embodiment, the cover ismade from polypropylene. In one advantageous embodiment, the cover isopaque to ambient light. The opaque characteristic can be obtained froma coating or from the material of construction. The cover has flange2162 which serves as a bonding surface with the base material.Advantageously, PSA on the base material provides the appropriate bondbetween the flange 2162 of the cover and the base material 2140.

A face stock 2170, advantageously constructed from a non-woven, flexiblematerial, is placed over the base material 2140. In an alternativeembodiment, a woven, flexible material is acceptable. In the presentembodiment, the face stock 2170 comprises 3M part no. 9908. The facestock preferably has an aperture 2171 to allow the cup portion of thecover 2160 to protrude through the face stock. The face stock 2170covers the flange portion 2162 (shown in dotted lines in FIG. 37) of thecover 2160. This assists in holding the cover 2160 firmly in place.Because the base material has PSA on the side to which the face stock isapplied, pressure applied to the face stock bonds the face stock withthe base material. In the present embodiment, the face stock 2170 alsohas PSA on one side (side down in FIG. 37). The face stock is cut suchthat the connector tab 2010 and the connector traces 2052 of the flexcircuit remain exposed. This manufacturing step is represented in anactivity block 3040 and is depicted in FIG. 37.

In addition, to a cutout 2172 in the face stock 2170 and the basematerial 2140 provide a slot on each side of the connector tab 2010 andthe connection traces end of the flex circuit assembly 2051. These slotsare adapted to receive walls of the connector receptacle 2060 (see FIG.29B) for stability.

Finally, the optical probe is die-cut to a final shape as depicted inFIG. 38 and represented in an activity block 3045 (FIG. 30). Themanufacturing method is complete, as represented within an activityblock 3055. Removal of the release liner 2003 on the base material 2140allows for placement on the digit of a pediatric or adult patient asdepicted in FIGS. 29A-29B.

Another embodiment of a low noise optical probe 2200 is depicted in FIG.40A. This embodiment is advantageous for use with neonates, as will befurther described below. FIG. 41 is a flow chart which details thegeneral method used for manufacturing a neonatal disposable opticalprobe 2200 in accordance with this second embodiment of the presentinvention.

As with the previous embodiment, the neonatal probe 2200 is constructedof several layers. A first tape layer 2210 is laid out as represented inan activity block 4010, and depicted in FIG. 42. Advantageously, thefirst tape layer 2210 is constructed from release liner material. Thefirst tape layer 2210 has adhesive portions on one side for adhesion tothe tissue material under test, as will be further understood below. Inthe present embodiment, the release liner is a conventional paper typerelease liner for the medical industry.

In a preferred embodiment, the first tape layer 2210 has a first portionof adhesive 2212 and a second portion of adhesive 2213 which provideadhesion in the area of the detector and emitters. In the presentembodiment, the adhesive portions 2212, 2213 are made from 3M partnumber MED 3044, which is a medical quality two-sided PSA material. Thismaterial is transparent to the wavelength of the emitter in the probe2200, and therefore, a thru hole is not required. However, a thru hole,such as the thru hole 2211 could be provided in one embodiment.

A second tape layer 2220 is placed over the first tape layer asrepresented in an activity block 4020, and depicted in FIG. 43. Thesecond tape layer 2220 includes an emitter aperture (thru hole) 2222 anda detector aperture 2224, which provide windows for the detector andemitters. In the present embodiment, the second tape layer is made froma non-woven face stock material, with PSA on one side. In the presentembodiment, the second tape layer 2220 comprises part number 9908, madeby 3M. In the illustration of FIG. 43, the adhesive side is up.

An optical cavity 2240 is placed onto the second tape as shown in FIG.43 and represented in an activity block 4030. One preferred embodimentof the optical cavity 2240 is illustrated in additional detail in FIGS.44A-C. FIG. 44A depicts a perspective view of the optical cavity 2240.FIG. 44B depicts a bottom plan view of the optical cavity 2240, and FIG.44C depicts a side cross-sectional view through 44C-44C of FIG. 44A. Aswith the embodiment of FIG. 39A-C, the optical cavity 2240 is made fromstyrene or ABS or the like in one embodiment. In one preferredembodiment, the optical cavity 2140 is coated with an optical coatingthat is opaque to ambient light. This can be on the inside walls of theoptical cavity or over the exterior walls of the optical cavity, or theentire optical cavity can be coated. The opaque coating advantageouslyprevents or minimizes the transmission of ambient light from thesurrounding environment which could be incident on the detector if theoptical cavity is not opaque to ambient light. As an alternative to anopaque coating, the optical cavity can be made from a material that isopaque to ambient light.

Advantageously, the optical cavity 2240 has a wedge-shaped ramp 2242 aspart of a rectangular receptacle 2244. The rectangular receptacle 2244is adapted to receive the detector end of a flex circuit, as furtherexplained below. The wedge-shaped ramp 2242 of the optical cavity 2240provides a ramp for a smooth transition for the flex circuit between thesurface of the second tape layer 2220 to a rectangular receptacle table2246.

Further illustrated in FIG. 44A are two side walls 2248 that extendalong the side border of the rectangular receptacle 2244 and an arcuateend wall 2250 that extends between the two side walls 2248. These wallshold the flex circuit in position such that the detector aligns properlywith a aperture 2252 in the optical cavity 2240. Preferably, the flexcircuit fits snugly between the side walls 2248.

In a preferred embodiment, the aperture 2252 has the configuration ofthe cavities describe above in general (e.g., cone-shaped, cylindricalin shape, conical in shape, etc.)

A flex circuit 2254 is depicted in detail in FIGS. 45A-B. As depicted inFIG. 45A, a flex circuit is formed on a flexible substrate 2255. In thepresent embodiment, the flexible substrate advantageously comprises 3Mil polyester (e.g., MYLAR™) with copper coating on 1 side. In thepresent embodiment, the copper coating is ½ OZ. copper coating. Thecircuit pattern is etched such that the circuit traces of copper remainon a signal side of the flex circuit 2254 after etching. From thisetching standpoint, the flex circuit 2254 is made in the same fashion asthe flex circuit assembly 2051 of the adult probe 2002.

Once the circuit is etched, it is placed on a bottom shielding layer2256, depicted in FIG. 45A. In one embodiment, the shielding comprises ametallized MYLAR™ shield, with one side metallized. The metallic side ispositioned against the back side of the flex circuit substrate 2255.Conductive PSA bonds the flex circuit substrate 2252 with the bottomshielding layer 2256 through connection 2251 connects the bottom shieldmetallization to ground from the ground trace 2253. The bottom shieldinglayer 2256 has an emitter aperture corresponding to the emitter aperture2252 in the optical cavity 2240 and the emitter aperture 2257 in theflex circuit 2254. The bottom shielding layer 2256 extends (extensionlabeled 2258 in FIG. 45A) beyond the detector end of the flex circuit2250. In an alternative embodiment, the back side of the flex circuit2254 has a metal coating, such as copper. This provides appropriateshielding. Thus, the first shielding layer could be eliminated in analternative embodiment.

A detector shield 2260, such as the detector shield 2110 of the probe2002 (FIG. 32), is bonded to the signal trace side of flex circuit 2254,as depicted in FIG. 45B. Next, a detector 2272 is placed using lowtemperature solder, as with the previous embodiment, such that thedetector field of view is through the grating 2261 in the detectorshield 2260. The detector shield 2260 is then folded over the detectorin order to provide a Faraday shield, as with the previous embodiment.

The extension 2258 of the first shielding layer 2256 is then folded overand conductive PSA is used to bond the metallized side of the bottomshielding layer 2256 to the detector shield 2260. This connects thedetector shield to ground. The emitter 2270 is also placed using the lowtemperature solder.

In one advantageous embodiment, a resistor 2262 is also placed either inparallel with the emitter or is provided with its own connection trace.The embodiment of FIG. 45A depicts an embodiment with a separateconnection trace 2263 for the resistor 2262.

A top shielding layer 2268 is placed to shield the signal side of theflex circuit, as depicted in FIG. 45C. In the present embodiment, thissecond shielding layer 2268 comprises the same material as the firstshielding layer 2256. The second shielding layer 2268 is bonded to thedetector shield 2260 using conductive PSA which couples the secondshielding layer 2268 to ground. The second shielding layer 2268 coversthe entire flex circuit and is bonded to the flex circuit 2254 usingPSA.

The flex circuit assembly 2254 of FIG. 45 used in the neonatal probe2200 is constructed with a unique V-configuration. The emitter 2270 isat the tip of one branch, a detector 2272 is at the tip of the otherbranch, and a connector tab 2274 (substantially the same as theconnector tab 2010) is attached at the base of the “V.”

The optical cavity 2240 is substantially the same as the optical cavity2150. In addition, the detector 2272 and the emitter 2270 aresubstantially the same as the detector 2120 and the emitter 2021.

Once the shielded flex circuit assembly 2254 is completed, the completedflex circuit assembly is placed onto the second tape 2220, as depictedin if FIG. 46. The flex circuit 2250 is positioned such that the emitter2270 and the detector 2272 have a field of view through the respectiveapertures 2222, 2224 in the second tape layer 2220.

Once the flex circuit assembly is placed, third and fourth layers oftape 2280, 2290 are placed over the flex circuit assembly 2254 asrepresented within an activity block 4040 and depicted in FIG. 47. Thethird and fourth tape layers 2280, 2290 are made from the non-woven facematerial such as that made by 3M as part number 9908. The third andfourth tape layers 2280, 2290 have PSA on the side which bonds to theassembly made up of the first tape layer 2210, the second tape layer2220 and the flex circuit assembly 2254. As depicted in FIG. 47, thefourth tape layer 2290 is configured to allow connection traces 2292 ofthe flex circuit to remain exposed.

Finally, the neonatal disposable probe 2200 is die-cut to a final shapeas represented within activity block 4050 and depicted in FIG. 48. Themanufacturing method is then complete as represented within an activityblock 4060.

FIGS. 40A and 40B illustrate the neonatal probe being attached to ababy's foot (shown in phantom). The finger is placed on the detectorbranch of the probe 2200. The emitter branch is then positioned so thatthe emitter 2270 is directly above the detector 2272 with the footin-between. An adhesive strap 2400 (which was die-cut from the firsttape layer 2210 and the third tape layer 2280) is then wrapped aroundthe foot to secure the relative position of the emitter 2270 anddetector 2272. It should be appreciated that the adhesive materialselected to coat the adhesive strap should not be so strong as to tearor bruise the skin of a newborn baby. The connector 2060 subsequentlyestablishes electrical connection between the probe 2200 and digitalsignal processing circuitry via the connector tab 2294.

The unique V-configuration of the neonatal probe embodiment of thepresent invention (e.g., as displayed in FIG. 49) is particularlyadvantageous for use in applications where the optical probe is used onneonates. The V-configuration allows the probe to be used on manydifferent sizes of monitoring sites (e.g., feet, hands, etc.) for aneonate. With conventional wrap-around embodiments, the spacing of thedetector and emitter is fixed, thus making the use of the probe fordifferent sized monitoring sites more difficult. In addition, theV-shaped design allows for the use of the probe on various body parts.For instance, the probe 2200 could be attached to the nose or ear of theneonate. The probe 2200 could also be used as a reflectance probe withthe probe attached to the forehead of the neonate, or other relativelyflat skin surface. Thus, the V-design provides for the adaptation of theprobe for many different places on the neonate body.

An alternative embodiment of the V-configuration is depicted in FIG. 49.In the embodiment depicted in FIG. 49, the adhesive extension 2400 (FIG.48) is not provided. In this embodiment, the probe can be used withconventional medical tape or the like, or can be provided such that theadhesive 2212, 2213 (FIG. 42) in the area of the detector and emitterhold the probe in place. Alternatively, a soft, spongy, hospital wrap(e.g., a POSEY wrap) 2498 can be configured to firmly hold the probe toa digit as depicted in FIG. 50.

Another embodiment of the method of making the neonatal probe isillustrated in FIGS. 51-55. An X-ray type view of the alternativeembodiment 2500 is depicted in FIG. 51. As illustrated in FIG. 51, theprobe 2500 has a detector 2502, an emitter 2504, a flex circuit 2506, alow noise cavity 2508 and a cover 2510 for the optical cavity 2508, topand base tapes 2512, 2514, an identification resistor 2516, thruconnections 2518, 2520, and a connection tab 2522. This embodiment ofthe probe is depicted without the tape extension, such as the extension2400 (FIG. 48), but could include a tape extension in one embodiment.The overall configuration of the finished probe 2500 is nearly identicalto the probe of FIG. 49. However, the shielding is different, theoptical cavity has a cover, and the probe 2500 is constructed using twotapes instead of four. The construction of this embodiment of the probe2500 is similar to the adult probe from the standpoint of the tape-up.

FIGS. 52A and 52B illustrate a base tape 2530 and the top tape 2540. Thebase tape 2530 has a detector component window 2532 and an emittercomponent window 2534. Advantageously, the component windows formapertures through the base tape 2530. Therefore, in one preferredembodiment, clear (i.e., transparent to the emitter wavelengths) windowmaterial portions 2536, 2538 are provided as a cover to the componentwindows 2532, 2534. In one embodiment, the clear window material is madefrom the 3M, Med 3044 described above. The MED 3044 is attached to theback-side (with reference to the illustration in FIG. 52A) of the basetape 2530 in order to provide adhesion to the tissue material undertest. Alternatively, the window material 2536, 2538 is non-adhesive, andcan be mounted to the up-side (with reference to the illustration inFIG. 53A) of the base tape.

In the present embodiment, the base tape 2530 is formed of a laminateformed of a first layer of non-woven face stock, such as that made by 3Mas part number 9908, and a second film, such as single-sided PSA filmsold by Coating Sciences, Inc. as P-341. The face stock has PSA on oneside. In the illustration of FIG. 52A, the PSA for the face stock is up.The second film of material is laminated to the first layer of non-wovenface stock. In the present embodiment, the second layer also has oneside with PSA. In the illustration of FIG. 52A, the PSA side of thesecond film is up. Accordingly, the side of the base tape 2530 depictedin FIG. 52A has PSA from the second film. In the present embodiment, thesecond film comprises a 1 Mil layer of Coating Sciences part numberP-341. The use of two layers provides improved isolation to the flexcircuit.

FIG. 52B illustrates the top tape 2540, which is also formed of the twolayers of material as with the base tape. In the illustration of FIG.52B, the adhesive side of the top tape is down and the face stock sideof the top tape 2540 is up. For the present embodiment, the top tape hasa cutout 2542 for the cover 2510 to the optical cavity 2508. The opticalcavity 2508 has the same configuration as the optical cavity 2240 FIG.44.

An appropriate cover 2510 is depicted in detail in FIG. 55A-C. The coveris cup-shaped to fit snugly about the optical cavity 2508. FIG. 55Adepicts a top view of the optical cover 2510. FIG. 55B depicts a sidecross sectional view through B-B in FIG. 55A. FIG. 55C depicts an endcross-sectional view through 55C-55C in FIG. 55A. In the presentembodiment, the cover 2510 is vacuum formed from styrene, and is coatedwith a light absorbing paint, such as black paint to reduce the effectsof ambient light.

FIG. 53A illustrates the signal side of an appropriate flex circuit 2506and FIG. 53B illustrates the back side (i.e., shield side in the thisembodiment) of the flex circuit 2506. As depicted in FIG. 54B, thesignal side of the flex circuit 2506 has signal traces, theidentification resistor 2516, and the two through connections 2518,2520. The flex circuit also has connection pads 2560, 2562 for thedetector 2502 and connection pads 2564, 2556 for the emitter 2504. Aswith the previous embodiments, the signal side of the flex circuit 2506has traces formed by etching away the metallic coating. The flex circuitis formed of the same materials as described for the previousembodiments of flex circuits.

FIG. 53B depicts the shield side of the flex circuit 2506. In thisembodiment, the flex circuit 2506 is a two-sided circuit, with theshield side coated, substantially in its entirety, with metal, such ascopper. By providing a metallic shield side, a separate shielding layeris not needed for the back of the flex circuit 2506. The throughconnections 2518, 2520 connect the shield side metal to the ground trace2510.

FIG. 54 illustrates a top shield 2570 for the flex circuit 2506. In thepresent embodiment, the top shield 2570 is formed from a metallizedMYLAR™ as with the shields for the previous embodiment. Prior toapplication of the top shield 2570, the detector 2502 and the emitter2504 are soldered to the connection pads 2560, 2562, 2564, 2566. Thenone end of a detector shield 2572, having the same configuration as thedetector shield 2260 (FIG. 45B) is connected to the shield side of theflex circuit 2506. In one embodiment, the connection is made with solderor conductive PSA.

The top shield 2570 is applied to the signal side of the flex circuit2506 (with the non-metallized side against the signal side of the flexcircuit) with PSA. The detector branch 2574 of the top shield 2570 islonger than a detector branch 2563 of the flex circuit 2506. Thus, thedetector branch 2574 is positioned such that the end of the detectorbranch 2574 covers the detector 2502. Conductive PSA 2576 is applied tothe end of the metallized side of the detector branch 2574. The detectorshield 2272 is folded over the top shield 2570 and connection is madevia the conductive PSA 2576. In this manner, top shield 2570 is coupledto ground via the connection detector shield 2572 which is connected toground via its connection to the shield side of the flex circuit 2506.

Once the flex circuit assembly 2506 is completed, it is placed on thebase tape 2530, with the detector 2502 and the emitter 2504 aligned withthe detector window 2532 and the emitter window 2534, respectively. Thedetector 2502 also is positioned in the rectangular receptacle table ofthe optical cavity 2508. The optical cavity cover 2510 is then placedover the optical cavity 2508. Finally, the top tape 2540 is placed overthe entire assembly with the cut-out for the optical cavity coveraligned with the cover 2510. The entire assembly is pressed to set thePSA adhesive on the base tape 2530 and the top tape 2540. The assemblyis then die cut to the shape depicted in FIG. 51.

This embodiment of the probe 2506 has the advantage of fewer assemblysteps, and therefore reduced cost. The use of the cover 2510 also allowsfor further isolation of the detector from ambient light. As discussedabove, the cover, as well as the optical cavity, can be made opaque toambient light, either through coatings or pigmented or otherwiseimpregnated materials.

In accordance with another embodiment of the invention, a reusable,low-noise, optical probe 2300 is constructed as depicted in FIG. 56. Theprobe 2300 comprises a padded, clip-on bracket 2305 which comfortablysecures the probe 2300 onto a patient's fingertip (not shown in FIG.56). The probe further includes a detector 2310 (shown in phantom) whichdetects optical radiation emitted by an emitter 2320 (also shown inphantom). An aperture 2330, which is substantially similar to theaperture 1020, is formed in the probe 2300 to provide the advantagesenumerated above with respect to the aperture 1020. Power to activatethe LED 2320, is provided via a connector cable 2340. The cable 2340also provides a return path for signals output by the detector 2310.Advantageously, the reusable probe 2300 can have a connector with asimilar configuration as the connector for the disposable probes, suchthat the instrument connector can be the same for use with disposableand reusable probes.

The probe of the present invention may be employed in any circumstancewhere a measurement of transmitted or reflected energy is to be made,including but not limited to measurements taken on a finger, an earlobe,a lip, or a forehead. Thus, there are numerous other embodimentsincluding, but not limited to, changes in the shape of the probe,changes in the materials out of which the probe is made including rigidand resilient materials, and changes in the shape, dimensions, andlocation of the chamber. Moreover, the chamber(s) may be coated, inwhole or in part, with reflective material to help direct energy ontothe detector. Furthermore, the probe of the present invention may beemployed in measurements of other types of energy. Depending upon thetype of energy which is most advantageously utilized in a measurement,the type of transmitter or receiver of energy may be changed. Theinvention may be embodied in other specific forms without departing fromits spirit or essential characteristics. The described embodiments areto be considered in all respects only as illustrative and notrestrictive. The scope of the invention is, therefore, indicated by theappended claims rather than by the foregoing description. All changeswhich come within the meaning and range of equivalency of the claims areto be embraced within their scope.

What is claimed is:
 1. A disposable optical probe comprising: a flexcircuit housing a plurality of conductors, at least one emitter and adetector, wherein at least some of the conductors electricallycommunicate with the at least one emitter and others of the conductorselectrically communicate with the detector, wherein the detector iscapable of detecting light attenuated by body tissue at a measurementsite, and wherein the flex circuit assembly also includes, first andsecond branches a cable connector portion, and an elongated neck portionelectrically and mechanically connecting the first and second branchesto the cable connector portion where each of the first and secondbranches diverges from one end of the elongated neck portion in agenerally V-shaped configuration and the cable connector portionterminates the other end, the elongated neck portion being substantiallylonger than either of the first and second branches, the first branchpositioning the at least one emitter and the second branch positioningthe detector, the branches cooperating to provide variability in adistance from the at least one emitter to the detector; and a disposableflexible wrap extending from an end of one of said branches andconfigured for positioning said assembly with respect to the body tissueand further configured for stabilizing said variability in said distanceand materially reducing the effect of light noise on the detector,wherein the disposable flexible wrap is capable of removably attachingsaid optical probe to the measurement site.
 2. The probe according toclaim 1, wherein said disposable flexible wrap comprises a soft wrap. 3.The probe according to claim 2, wherein the soft wrap is affixed using ahook-and-loop material.
 4. The probe according to claim 2, wherein saidsoft wrap comprises a POSEY wrap.
 5. The probe according to claim 2,wherein the soft wrap includes at least one aperture positioning atleast one of the first and second branches.
 6. The probe according toclaim 1, wherein said measurement site comprises body tissue of one ofan adult patient, a pediatric patient, an infant patient, and a neonatalpatient.
 7. The probe according to claim 6, wherein the tissue comprisesone of a forehead, a digit, a heel, and a foot.
 8. The probe accordingto claim 1, wherein said disposable flexible wrap comprises a tape.
 9. Amethod of assembling a noninvasive sensor configured to output signalsindicative of light attenuated by body tissue, the method comprising:acquiring a flex circuit assembly housing a plurality of conductors,ones of said conductors electrically communicating with at least oneemitter and others electrically communicate with the detector, thedetector capable of detecting light attenuated by body tissue at ameasurement site, and wherein the flex circuit assembly also includesfirst and second branches, a cable connector portion, and an elongatedneck portion electrically and mechanically connecting the first andsecond branches to the cable connector portion where each of the firstand second branches diverges from one end of the elongated neck portionin a generally V-shaped configuration and the cable connector portionterminates the other end, the elongated neck portion being substantiallylonger than either of the first and second branches, the first branchpositioning the at least one emitter and the second branch positioningthe detector, the branches cooperating to provide variability in adistance from the at least one emitter to the detector; and acquiring adisposable flexible wrap and configuring said wrap to extend from an endof one of said branches; positioning said assembly with respect to thebody tissue using the wrap; and stabilizing said variability in saiddistance and materially reducing the effect of light noise on thedetector, wherein the disposable flexible wrap is capable of removablyattaching said optical probe to the measurement site.
 10. The methodaccording to claim 9, wherein said disposable flexible wrap comprises asoft wrap.
 11. The method according to claim 10, wherein the soft wrapis removably attachable using a hook-and-loop material.
 12. The methodaccording to claim 10, wherein said soft wrap comprises a POSEY wrap.13. The method according to claim 10, wherein the soft wrap includes atleast one aperture positioning at least one of the first and secondbranches.
 14. The method according to claim 9, wherein said measurementsite comprises body tissue of one of an adult patient, a pediatricpatient, an infant patient, and a neonatal patient.
 15. The methodaccording to claim 14, wherein the tissue comprises one of a forehead, adigit, a heel, and a foot.
 16. The method according to claim 9, whereinsaid disposable flexible wrap comprises a tape.